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/index.ts

@@ -0,0 +1,66 @@
+/**
+ * Per-type content-tab descriptors for the service page skeleton.
+ *
+ * Each entry names a tab and its component. The service page renders
+ * `[Overview, ...contentTabs(type), Widgets, Config]`.
+ */
+import type { ComponentType } from "react";
+import type { ServiceInstance } from "../../types";
+import { OverviewTab } from "./stubs";
+import { AlertsTab } from "./AlertsTab";
+import { LinksTab } from "./LinksTab";
+import { MetricsTab } from "./MetricsTab";
+import { MediaTab } from "./MediaTab";
+import { RequestsTab } from "./RequestsTab";
+import { FilesTab } from "./FilesTab";
+import { ActionsTab } from "./ActionsTab";
+import { JobsTab } from "./JobsTab";
+import { UsersTab } from "./UsersTab";
+import { MessagingTab } from "./MessagingTab";
+
+export type ServiceTabComponent = ComponentType<{ instance: ServiceInstance }>;
+
+export interface ContentTab {
+	label: string;
+	Component: ServiceTabComponent;
+}
+
+/** Overview tab (shared across all service types). */
+export const OVERVIEW_TAB: ContentTab = {
+	label: "Overview",
+	Component: OverviewTab,
+};
+
+/**
+ * Returns the type-specific content tabs for a service type.
+ * Types with no operational content return `[]` (only Overview + Widgets + Config).
+ */
+export function serviceContentTabs(serviceType: string): ContentTab[] {
+	switch (serviceType) {
+		case "jellyfin":
+			return [
+				{ label: "Media", Component: MediaTab },
+				{ label: "Requests", Component: RequestsTab },
+			];
+		case "ssh_tasks":
+			return [
+				{ label: "Files", Component: FilesTab },
+				{ label: "Actions", Component: ActionsTab },
+			];
+		case "backups":
+			return [{ label: "Jobs", Component: JobsTab }];
+		case "authentik":
+			return [
+				{ label: "Users", Component: UsersTab },
+				{ label: "Messaging", Component: MessagingTab },
+			];
+		case "alertmanager":
+			return [{ label: "Alerts", Component: AlertsTab }];
+		case "grafana":
+			return [{ label: "Links", Component: LinksTab }];
+		case "prometheus":
+			return [{ label: "Metrics", Component: MetricsTab }];
+		default:
+			return [];
+	}
+}