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/hooks/useAuthentik.ts

@@ -0,0 +1,43 @@
+/** Hooks for the Authentik directory + messaging tabs. */
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import {
+	fetchAuthentikMessageStatus,
+	fetchAuthentikUsers,
+	sendAuthentikMessage,
+} from "../api/authentik";
+
+export function useAuthentikUsers(
+	serviceId: string,
+	params: { search?: string; page?: number; page_size?: number },
+) {
+	return useQuery({
+		queryKey: ["authentik", "users", serviceId, params],
+		queryFn: () => fetchAuthentikUsers(serviceId, params),
+		staleTime: 10_000,
+	});
+}
+
+export function useSendAuthentikMessage(serviceId: string) {
+	const queryClient = useQueryClient();
+	return useMutation({
+		mutationFn: (input: {
+			recipient_emails: string[];
+			subject: string;
+			html_body: string;
+		}) => sendAuthentikMessage(serviceId, input),
+		onSuccess: () => {
+			queryClient.invalidateQueries({
+				queryKey: ["authentik", "message-status", serviceId],
+			});
+		},
+	});
+}
+
+export function useAuthentikMessageStatus(serviceId: string) {
+	return useQuery({
+		queryKey: ["authentik", "message-status", serviceId],
+		queryFn: () => fetchAuthentikMessageStatus(serviceId),
+		refetchInterval: 5_000,
+		staleTime: 0,
+	});
+}

frontend/src/hooks/useDashboards.ts

@@ -0,0 +1,47 @@
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import {
+	createDashboard,
+	deleteDashboard,
+	fetchDashboardBySlug,
+	fetchDashboards,
+	updateDashboard,
+	type NamedDashboardInput,
+} from "../api/dashboards";
+
+export function useDashboards() {
+	return useQuery({
+		queryKey: ["dashboards"],
+		queryFn: fetchDashboards,
+		staleTime: 30 * 1000,
+	});
+}
+
+export function useDashboardBySlug(slug: string | undefined) {
+	return useQuery({
+		queryKey: ["dashboards", "slug", slug],
+		queryFn: () => fetchDashboardBySlug(slug!),
+		enabled: !!slug,
+		staleTime: 30 * 1000,
+	});
+}
+
+export function useSaveDashboard() {
+	const queryClient = useQueryClient();
+	return useMutation({
+		mutationFn: (input: NamedDashboardInput) =>
+			input.id ? updateDashboard(input) : createDashboard(input),
+		onSuccess: () => {
+			queryClient.invalidateQueries({ queryKey: ["dashboards"] });
+		},
+	});
+}
+
+export function useDeleteDashboard() {
+	const queryClient = useQueryClient();
+	return useMutation({
+		mutationFn: (id: string) => deleteDashboard(id),
+		onSuccess: () => {
+			queryClient.invalidateQueries({ queryKey: ["dashboards"] });
+		},
+	});
+}

frontend/src/hooks/useUsers.ts

@@ -1,11 +0,0 @@
-import { useQuery } from "@tanstack/react-query";
-import { fetchUsers } from "../api/client";
-import type { UserDirectoryResponse } from "../types";
-
-export function useUsers(jellyfinServiceId?: string) {
-	return useQuery<UserDirectoryResponse>({
-		queryKey: ["users", jellyfinServiceId ?? "default"],
-		queryFn: () => fetchUsers(jellyfinServiceId),
-		staleTime: 30_000,
-	});
-}