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.

backend/tests/test_dashboards.py

@@ -0,0 +1,97 @@
+"""Tests for named-dashboards CRUD + slug uniqueness."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from fastapi.testclient import TestClient
+
+from media_library_viewer_api.dependencies import get_settings_store
+from media_library_viewer_api.main import app
+from media_library_viewer_api.services.settings_store import SettingsStore
+
+
+def _client(tmp_path: Path) -> TestClient:
+    store = SettingsStore(tmp_path / "settings.sqlite")
+    app.dependency_overrides[get_settings_store] = lambda: store
+    client = TestClient(app)
+    client.store = store  # type: ignore[attr-defined]
+    return client
+
+
+def test_create_and_list_dashboards(tmp_path: Path):
+    client = _client(tmp_path)
+    try:
+        resp = client.post(
+            "/api/dashboards",
+            json={"label": "Storage Overview", "payload": {"widgets": []}},
+        )
+        assert resp.status_code == 200
+        created = resp.json()
+        assert created["label"] == "Storage Overview"
+        assert created["slug"] == "storage-overview"
+        assert created["payload"] == {"widgets": []}
+
+        listed = client.get("/api/dashboards").json()
+        assert len(listed) == 1
+        assert listed[0]["id"] == created["id"]
+    finally:
+        app.dependency_overrides.clear()
+
+
+def test_update_dashboard(tmp_path: Path):
+    client = _client(tmp_path)
+    try:
+        created = client.post("/api/dashboards", json={"label": "First"}).json()
+        updated = client.put(
+            f"/api/dashboards/{created['id']}",
+            json={"label": "Renamed", "payload": {"widgets": ["w1"]}},
+        ).json()
+        assert updated["label"] == "Renamed"
+        assert updated["payload"] == {"widgets": ["w1"]}
+        assert updated["slug"] == "renamed"
+    finally:
+        app.dependency_overrides.clear()
+
+
+def test_delete_dashboard(tmp_path: Path):
+    client = _client(tmp_path)
+    try:
+        created = client.post("/api/dashboards", json={"label": "Temp"}).json()
+        resp = client.delete(f"/api/dashboards/{created['id']}")
+        assert resp.status_code == 200
+        assert client.get("/api/dashboards").json() == []
+    finally:
+        app.dependency_overrides.clear()
+
+
+def test_slug_collision_appends_suffix(tmp_path: Path):
+    client = _client(tmp_path)
+    try:
+        first = client.post("/api/dashboards", json={"label": "Overview"}).json()
+        second = client.post("/api/dashboards", json={"label": "Overview"}).json()
+        assert first["slug"] == "overview"
+        assert second["slug"] == "overview-2"
+    finally:
+        app.dependency_overrides.clear()
+
+
+def test_explicit_slug_respected(tmp_path: Path):
+    client = _client(tmp_path)
+    try:
+        created = client.post(
+            "/api/dashboards",
+            json={"label": "My Dashboard", "slug": "custom-slug"},
+        ).json()
+        assert created["slug"] == "custom-slug"
+    finally:
+        app.dependency_overrides.clear()
+
+
+def test_update_nonexistent_returns_404(tmp_path: Path):
+    client = _client(tmp_path)
+    try:
+        resp = client.put("/api/dashboards/nope", json={"label": "X"})
+        assert resp.status_code == 404
+    finally:
+        app.dependency_overrides.clear()