Rebase services-as-hub-ia onto mobile-responsive-parity

Combine both branches into a single coherent branch:
- Full mobile responsive parity (useIsMobile, MobileCardRow, SheetForm,
  .mobile-touch-target, mobile cards, SheetForm forms, 44px targets,
  dirty-state confirm, TablePagination, refetchIntervalInBackground).
- Full services-as-hub IA (data-driven nav, service-page tab skeleton,
  new service types, Authentik directory + messaging, named dashboards,
  legacy routes 404, Observability split, Jellyseerr absorbed).

Enhancement: service tabs now use mobile-parity primitives:
- MediaTab: MobileCardRow below md (title/size/HDR/library/year) +
  TablePagination; DataTable at md+ (desktop branch preserved).
- FilesTab: MobileCardRow below md (name/type/size/modified) +
  handleRowClick; DataTable at md+.
- ServicePage: SheetForm branch below md (open-on-mount, sticky header
  + save bar, cancel navigates back to /services, dirty-state guard).
- Dashboard: single-column + section anchors below md (from mobile-parity)
  + empty-state CTA (from services-hub).
- App.tsx: useIsMobile() replaces inline matchMedia (from mobile-parity)
  + data-driven useNavItems (from services-hub).
- Backup tables (BackupAlerts/Jobs/Runs) already have MobileCardRow from
  mobile-parity; JobsTab inherits mobile behavior through its sub-components.

Conflict resolutions:
- Backend: entirely from services-hub (mobile didn't touch it).
- Deleted pages (Media/FileBrowser/Actions/Users/UsersPage/Applications/
  ObservabilityPage/BackupsPage + hooks/useUsers + tests): kept deleted
  (services-hub deleted them; content moved into service tabs).
- New service-tabs/*: from services-hub, enhanced with mobile patterns.
- App.tsx: services-hub's data-driven nav + mobile-parity's useIsMobile.
- Dashboard.tsx: merged (services-hub CTA + mobile-parity sections/anchors).
- ServicePage.tsx: services-hub's tab skeleton + mobile-parity's SheetForm.
- Primitives (useIsMobile/mobile-card/sheet-form/etc.): from mobile-parity.

117 frontend tests pass (mobile-parity's 122 - 5 deleted page tests +
services-hub's new tab/dashboard tests); 271 backend tests pass; lint/
build green both sides.

frontend/src/pages/service-tabs/RequestsTab.tsx

@@ -0,0 +1,64 @@
+/**
+ * RequestsTab — Jellyseerr request-management surface on the Jellyfin page.
+ *
+ * Jellyseerr was absorbed into Jellyfin config (jellyseerr_url +
+ * jellyseerr_api_key) in Slice 1. This tab reads those config fields. When
+ * configured, it shows the URL and a placeholder (no requests backend endpoint
+ * exists yet — building one is out of scope for this slice). When not
+ * configured, it shows an empty-state CTA directing the user to add the fields
+ * to the Jellyfin config.
+ */
+import type { ServiceInstance } from "../../types";
+import { Alert, AlertDescription } from "@/components/ui/alert";
+import { ExternalLink } from "lucide-react";
+
+export function RequestsTab({ instance }: { instance: ServiceInstance }) {
+	const jellyseerrUrl = String(
+		(instance.config as Record<string, unknown>).jellyseerr_url ?? "",
+	).trim();
+	const jellyseerrApiKey = String(
+		(instance.config as Record<string, unknown>).jellyseerr_api_key ?? "",
+	).trim();
+
+	if (!jellyseerrUrl || !jellyseerrApiKey) {
+		return (
+			<Alert>
+				<AlertDescription>
+					Jellyseerr is not configured for this Jellyfin instance. Add
+					<code className="mx-1 rounded bg-muted px-1 py-0.5 text-xs">
+						jellyseerr_url
+					</code>
+					and
+					<code className="mx-1 rounded bg-muted px-1 py-0.5 text-xs">
+						jellyseerr_api_key
+					</code>
+					to the Jellyfin config (Config tab) to enable request management.
+				</AlertDescription>
+			</Alert>
+		);
+	}
+
+	return (
+		<div className="flex flex-col gap-4">
+			<div className="flex items-center gap-2">
+				<h3 className="text-sm font-semibold">Jellyseerr</h3>
+				<a
+					href={jellyseerrUrl}
+					target="_blank"
+					rel="noopener noreferrer"
+					className="inline-flex items-center gap-1 text-sm text-primary hover:underline"
+				>
+					{jellyseerrUrl}
+					<ExternalLink className="size-3.5" />
+				</a>
+			</div>
+			<Alert>
+				<AlertDescription>
+					Jellyseerr is configured. The requests view will show pending and
+					recently fulfilled media requests. (This surface is under
+					development.)
+				</AlertDescription>
+			</Alert>
+		</div>
+	);
+}