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/__tests__/UsersTab.test.tsx

@@ -0,0 +1,61 @@
+import { describe, it, expect, vi } from "vitest";
+import { render, screen } from "@testing-library/react";
+import { UsersTab } from "../UsersTab";
+import type { ServiceInstance } from "../../../types";
+
+const instance: ServiceInstance = {
+	id: "auth-1",
+	service_type: "authentik",
+	name: "Main Authentik",
+	config: { base_url: "https://auth.example.com", timeout_seconds: 10 },
+	secrets_set: { api_token: true },
+	enabled: true,
+	created_at: 1_700_000_000,
+	updated_at: 1_700_000_000,
+};
+
+vi.mock("../../../hooks/useAuthentik", () => ({
+	useAuthentikUsers: vi.fn(() => ({
+		data: {
+			items: [
+				{
+					pk: 1,
+					username: "alice",
+					name: "Alice",
+					email: "alice@example.com",
+					is_active: true,
+				},
+				{
+					pk: 2,
+					username: "bob",
+					name: "Bob",
+					email: "bob@example.com",
+					is_active: false,
+				},
+			],
+			total: 2,
+			page: 1,
+			page_size: 25,
+		},
+		isLoading: false,
+	})),
+}));
+
+describe("UsersTab", () => {
+	it("renders the directory table with users", () => {
+		render(<UsersTab instance={instance} />);
+		expect(screen.getByText("Alice")).toBeInTheDocument();
+		expect(screen.getByText("bob")).toBeInTheDocument();
+		expect(screen.getByText("alice@example.com")).toBeInTheDocument();
+		expect(screen.getByText("Active")).toBeInTheDocument();
+		expect(screen.getByText("Inactive")).toBeInTheDocument();
+	});
+
+	it("renders search input and pagination", () => {
+		render(<UsersTab instance={instance} />);
+		expect(screen.getByPlaceholderText("Search users…")).toBeInTheDocument();
+		expect(screen.getByText(/2 users/)).toBeInTheDocument();
+		expect(screen.getByText("Previous")).toBeInTheDocument();
+		expect(screen.getByText("Next")).toBeInTheDocument();
+	});
+});