Mobile Users + Backups tables: stacked cards + selection (Slice 5)

Below md, the Users directory and the three Backups tables render as
MobileCardRow cards:

- UsersPage: display name primary; username/activity/email fields. Each
  card carries a selection checkbox (44px via mobile-touch-target) in the
  actions slot with stopPropagation so toggling selection does not open
  the drawer; card-body tap still opens the drawer.
- BackupAlertsTable: alert message primary; severity/type/created fields;
  Acknowledge action preserved in actions slot.
- BackupJobsTable: job name primary; source/schedule/last-status fields
  (joins latestRuns into a JobCardRow).
- BackupRunsTable: run job_id primary; status/duration/size/started fields;
  status-filter Select renders above both layouts (preserved on mobile).

Desktop (md+) is byte-for-byte identical for all four components -- the
UsersPage diff is dominated by re-indenting the existing Table into the
isMobile ternary else branch.

Fix from Slice 5 review: MobileCardRow now renders the clickable card as
<div role=button tabIndex=0> with Enter/Space keyboard handling instead
of <button>, so nesting a Radix Checkbox (which renders a <button>) in
the actions slot produces valid HTML. The desktop-parity argument for
<button>-in-<button> did not hold (desktop rows are <tr>, not buttons).

Cross-cutting: useIsMobile hardened with typeof window.matchMedia guard
(safe in real browsers; only changes jsdom crash -> false). The file-local
900px compose hook was renamed useComposeViewport to avoid collision with
the shared 768px useIsMobile.

Tests: BackupJobsTable test file added (was untested), UsersPage mobile
selection round-trip + stopPropagation, mobile card render across all
four components. 105 tests pass; lint/build green.

Refs openspec/changes/mobile-responsive-parity/ (spec R3, tasks slice 5).

frontend/src/pages/UsersPage.impl.tsx

@@ -51,8 +51,13 @@ import {
 import { cn } from "@/lib/utils";
 import { MetricCard } from "../components/MetricCard";
 import { SessionActivityPanel } from "../components/SessionActivityPanel";
+import {
+	MobileCardRow,
+	type MobileCardField,
+} from "@/components/ui/mobile-card";
 import { useUsers } from "../hooks/useUsers";
 import { useActivity } from "../hooks/useDashboard";
+import { useIsMobile } from "../hooks/useIsMobile";
 import { useSendUserMessage } from "../hooks/useSendUserMessage";
 import { useUserMessageQueueStatus } from "../hooks/useUserMessageQueueStatus";
 import type { UserDirectoryItem } from "../types";
@@ -63,9 +68,9 @@ import {
 	type UserStateItem,
 } from "../userState";
 
-// Replaces MUI `useMediaQuery` (a 6b-owned component) with a dependency-free
-// matchMedia hook for the compose dialog's mobile fullScreen behavior.
-function useIsMobile(query = "(max-width: 900px)") {
+// Local breakpoint for the compose dialog (slice 6b uses 900px for fullScreen).
+// The shared `useIsMobile` from hooks/ (768px) drives the directory table branch.
+function useComposeViewport(query = "(max-width: 900px)") {
 	const [mobile, setMobile] = useState(() =>
 		typeof window !== "undefined" && typeof window.matchMedia === "function"
 			? window.matchMedia(query).matches
@@ -102,11 +107,35 @@ function activityBadgeVariant(
 
 const DEFAULT_HTML_BODY = "<p>Hello,</p><p> </p><p>Best,<br />Manage</p>";
 
+// Mobile card fields (spec R3.2): display name is primary; username, activity
+// badge, and email give the at-a-glance info for scanning users on a phone.
+// See OpenSpec change `mobile-responsive-parity`, tasks slice 5.1.
+const userCardFields: MobileCardField<UserStateItem>[] = [
+	{ key: "name", label: "Name", render: (r) => userLabel(r), primary: true },
+	{
+		key: "username",
+		label: "Username",
+		render: (r) =>
+			r.username && r.username !== r.display_name ? r.username : r.jellyfin_id,
+	},
+	{
+		key: "activity",
+		label: "Activity",
+		render: (r) => (
+			<Badge variant={activityBadgeVariant(r.activity_label)}>
+				{r.activity_label}
+			</Badge>
+		),
+	},
+	{ key: "email", label: "Email", render: (r) => r.email || "—" },
+];
+
 export function UsersPage() {
 	const { data, isError, error } = useUsers();
 	const { data: activity } = useActivity();
 	const queueStatusQuery = useUserMessageQueueStatus();
 	const sendUserMessage = useSendUserMessage();
+	const isComposeMobile = useComposeViewport();
 	const isMobile = useIsMobile();
 	const [search, setSearch] = useState("");
 	const [searchParams, setSearchParams] = useSearchParams();
@@ -479,154 +508,183 @@ export function UsersPage() {
 					</div>
 
 					<div className="max-h-[660px] overflow-auto rounded-lg border">
-						<Table aria-label="Users table">
-							<TableHeader>
-								<TableRow>
-									<TableHead className={cn(thBase, "w-14 p-2")}>
-										<Checkbox
-											checked={allVisibleSelected}
-											aria-label="Select all visible users"
-											onCheckedChange={(checked) =>
-												toggleVisibleSelection(checked === true)
-											}
-										/>
-									</TableHead>
-									<TableHead className={thBase}>User</TableHead>
-									<TableHead className={thBase}>Email</TableHead>
-									<TableHead className={cn(thBase, "w-[132px] text-center")}>
-										Activity
-									</TableHead>
-									<TableHead
-										className={cn(
-											thBase,
-											"hidden w-[140px] text-center md:table-cell",
-										)}
-									>
-										Type
-									</TableHead>
-									<TableHead className={cn(thBase, "w-[132px] text-center")}>
-										Jellyseerr
-									</TableHead>
-									<TableHead
-										className={cn(
-											thBase,
-											"hidden w-[120px] text-center md:table-cell",
-										)}
-									>
-										Role
-									</TableHead>
-									<TableHead className={thBase}>Permissions</TableHead>
-									<TableHead
-										className={cn(
-											thBase,
-											"hidden w-24 text-center md:table-cell",
-										)}
-									>
-										Reqs
-									</TableHead>
-									<TableHead
-										className={cn(
-											thBase,
-											"hidden w-[120px] text-center md:table-cell",
-										)}
-									>
-										Contact
-									</TableHead>
-								</TableRow>
-							</TableHeader>
-							<TableBody>
-								{filteredRows.map((row) => {
-									const linked =
-										row.jellyseerr_user_id !== null &&
-										row.jellyseerr_user_id !== undefined;
-									const checked = selectedIdSet.has(row.jellyfin_id);
-									return (
-										<TableRow
-											key={row.jellyfin_id}
-											data-state={
-												checked || selectedUser?.jellyfin_id === row.jellyfin_id
-													? "selected"
-													: undefined
-											}
-											className="cursor-pointer"
-											onClick={() => setSearchParams({ user: row.jellyfin_id })}
+						{isMobile ? (
+							<div className="p-3">
+								<MobileCardRow
+									rows={filteredRows}
+									fields={userCardFields}
+									getRowId={(r) => r.jellyfin_id}
+									onRowClick={(r) => setSearchParams({ user: r.jellyfin_id })}
+									actions={(r) => {
+										const checked = selectedIdSet.has(r.jellyfin_id);
+										return (
+											<Checkbox
+												checked={checked}
+												aria-label={`Select ${userLabel(r)}`}
+												className="mobile-touch-target"
+												onClick={(e) => e.stopPropagation()}
+												onCheckedChange={() =>
+													toggleUserSelected(r.jellyfin_id)
+												}
+											/>
+										);
+									}}
+								/>
+							</div>
+						) : (
+							<Table aria-label="Users table">
+								<TableHeader>
+									<TableRow>
+										<TableHead className={cn(thBase, "w-14 p-2")}>
+											<Checkbox
+												checked={allVisibleSelected}
+												aria-label="Select all visible users"
+												onCheckedChange={(checked) =>
+													toggleVisibleSelection(checked === true)
+												}
+											/>
+										</TableHead>
+										<TableHead className={thBase}>User</TableHead>
+										<TableHead className={thBase}>Email</TableHead>
+										<TableHead className={cn(thBase, "w-[132px] text-center")}>
+											Activity
+										</TableHead>
+										<TableHead
+											className={cn(
+												thBase,
+												"hidden w-[140px] text-center md:table-cell",
+											)}
 										>
-											<TableCell className="w-14 p-2">
-												<Checkbox
-													checked={checked}
-													aria-label={`Select ${userLabel(row)}`}
-													onClick={(event) => event.stopPropagation()}
-													onCheckedChange={() =>
-														toggleUserSelected(row.jellyfin_id)
-													}
-												/>
-											</TableCell>
-											<TableCell>
-												<div className="flex items-center gap-3 min-w-0">
-													<Avatar className="size-9">
-														<AvatarImage
-															src={row.avatar || undefined}
-															alt={userLabel(row)}
-														/>
-														<AvatarFallback>
-															{userLabel(row).charAt(0).toUpperCase()}
-														</AvatarFallback>
-													</Avatar>
-													<div className="min-w-0">
-														<div className="truncate font-semibold leading-tight">
-															{userLabel(row)}
-														</div>
-														<div className="truncate text-xs text-muted-foreground">
-															{row.username && row.username !== row.display_name
-																? row.username
-																: row.jellyfin_id}
+											Type
+										</TableHead>
+										<TableHead className={cn(thBase, "w-[132px] text-center")}>
+											Jellyseerr
+										</TableHead>
+										<TableHead
+											className={cn(
+												thBase,
+												"hidden w-[120px] text-center md:table-cell",
+											)}
+										>
+											Role
+										</TableHead>
+										<TableHead className={thBase}>Permissions</TableHead>
+										<TableHead
+											className={cn(
+												thBase,
+												"hidden w-24 text-center md:table-cell",
+											)}
+										>
+											Reqs
+										</TableHead>
+										<TableHead
+											className={cn(
+												thBase,
+												"hidden w-[120px] text-center md:table-cell",
+											)}
+										>
+											Contact
+										</TableHead>
+									</TableRow>
+								</TableHeader>
+								<TableBody>
+									{filteredRows.map((row) => {
+										const linked =
+											row.jellyseerr_user_id !== null &&
+											row.jellyseerr_user_id !== undefined;
+										const checked = selectedIdSet.has(row.jellyfin_id);
+										return (
+											<TableRow
+												key={row.jellyfin_id}
+												data-state={
+													checked ||
+													selectedUser?.jellyfin_id === row.jellyfin_id
+														? "selected"
+														: undefined
+												}
+												className="cursor-pointer"
+												onClick={() =>
+													setSearchParams({ user: row.jellyfin_id })
+												}
+											>
+												<TableCell className="w-14 p-2">
+													<Checkbox
+														checked={checked}
+														aria-label={`Select ${userLabel(row)}`}
+														onClick={(event) => event.stopPropagation()}
+														onCheckedChange={() =>
+															toggleUserSelected(row.jellyfin_id)
+														}
+													/>
+												</TableCell>
+												<TableCell>
+													<div className="flex items-center gap-3 min-w-0">
+														<Avatar className="size-9">
+															<AvatarImage
+																src={row.avatar || undefined}
+																alt={userLabel(row)}
+															/>
+															<AvatarFallback>
+																{userLabel(row).charAt(0).toUpperCase()}
+															</AvatarFallback>
+														</Avatar>
+														<div className="min-w-0">
+															<div className="truncate font-semibold leading-tight">
+																{userLabel(row)}
+															</div>
+															<div className="truncate text-xs text-muted-foreground">
+																{row.username &&
+																row.username !== row.display_name
+																	? row.username
+																	: row.jellyfin_id}
+															</div>
 														</div>
 													</div>
-												</div>
-											</TableCell>
-											<TableCell>
-												<div className="truncate font-medium">
-													{row.email || "—"}
-												</div>
-											</TableCell>
-											<TableCell className="text-center">
-												<Badge
-													variant={activityBadgeVariant(row.activity_label)}
-												>
-													{row.activity_label}
-												</Badge>
-											</TableCell>
-											<TableCell className="hidden text-center md:table-cell">
-												<Badge variant="outline">{row.user_type_label}</Badge>
-											</TableCell>
-											<TableCell className="text-center">
-												<Badge variant={linked ? "success" : "secondary"}>
-													{linked
-														? `Linked #${row.jellyseerr_user_id}`
-														: "Base only"}
-												</Badge>
-											</TableCell>
-											<TableCell className="hidden text-center md:table-cell">
-												<Badge variant="outline">{row.role}</Badge>
-											</TableCell>
-											<TableCell className="whitespace-normal">
-												{row.permissions_label}
-											</TableCell>
-											<TableCell className="hidden text-center font-semibold md:table-cell">
-												{row.request_count ?? "—"}
-											</TableCell>
-											<TableCell className="hidden text-center md:table-cell">
-												<Badge
-													variant={row.contactable ? "success" : "secondary"}
-												>
-													{row.contactable ? "Yes" : "No"}
-												</Badge>
-											</TableCell>
-										</TableRow>
-									);
-								})}
-							</TableBody>
-						</Table>
+												</TableCell>
+												<TableCell>
+													<div className="truncate font-medium">
+														{row.email || "—"}
+													</div>
+												</TableCell>
+												<TableCell className="text-center">
+													<Badge
+														variant={activityBadgeVariant(row.activity_label)}
+													>
+														{row.activity_label}
+													</Badge>
+												</TableCell>
+												<TableCell className="hidden text-center md:table-cell">
+													<Badge variant="outline">{row.user_type_label}</Badge>
+												</TableCell>
+												<TableCell className="text-center">
+													<Badge variant={linked ? "success" : "secondary"}>
+														{linked
+															? `Linked #${row.jellyseerr_user_id}`
+															: "Base only"}
+													</Badge>
+												</TableCell>
+												<TableCell className="hidden text-center md:table-cell">
+													<Badge variant="outline">{row.role}</Badge>
+												</TableCell>
+												<TableCell className="whitespace-normal">
+													{row.permissions_label}
+												</TableCell>
+												<TableCell className="hidden text-center font-semibold md:table-cell">
+													{row.request_count ?? "—"}
+												</TableCell>
+												<TableCell className="hidden text-center md:table-cell">
+													<Badge
+														variant={row.contactable ? "success" : "secondary"}
+													>
+														{row.contactable ? "Yes" : "No"}
+													</Badge>
+												</TableCell>
+											</TableRow>
+										);
+									})}
+								</TableBody>
+							</Table>
+						)}
 					</div>
 				</div>
 			</div>
@@ -766,7 +824,7 @@ export function UsersPage() {
 				<DialogContent
 					className={cn(
 						"flex max-h-[90dvh] flex-col gap-0 overflow-hidden p-0 sm:max-w-2xl",
-						isMobile &&
+						isComposeMobile &&
 							"inset-0 max-h-none max-w-none translate-x-0 translate-y-0 rounded-none",
 					)}
 				>