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/src/media_library_viewer_api/routers/backups.py

@@ -15,7 +15,23 @@ from ..services.settings_store import SettingsStore, get_settings_store
 router = APIRouter(prefix="/api/backups", tags=["backups"])
 
 
-def _get_or_create_job(store: SettingsStore, report: BackupReportRequest) -> dict[str, Any]:
+def _resolve_backup_service_id(store: SettingsStore, explicit: str | None = None) -> str:
+    """Return the service_id for backup attribution.
+
+    First-wins: if no explicit service_id is given, pick the first enabled
+    ``backups`` service instance (spec R6.1). Returns an empty string when
+    none is configured (backward-compatible with pre-service reports).
+    """
+    if explicit:
+        return explicit
+    candidates = store.list_services("backups")
+    for svc in candidates:
+        if svc.get("enabled"):
+            return svc["id"]
+    return ""
+
+
+def _get_or_create_job(store: SettingsStore, report: BackupReportRequest, service_id: str = "") -> dict[str, Any]:
     job = store.get_backup_job_by_name(report.name)
     if not job:
         job = store.upsert_backup_job(
@@ -24,6 +40,7 @@ def _get_or_create_job(store: SettingsStore, report: BackupReportRequest) -> dic
                 "source": report.source,
                 "target": report.target,
                 "schedule_interval_seconds": report.schedule_interval_seconds,
+                "service_id": service_id,
             }
         )
     elif report.schedule_interval_seconds:
@@ -34,6 +51,7 @@ def _get_or_create_job(store: SettingsStore, report: BackupReportRequest) -> dic
                 "source": report.source,
                 "target": report.target,
                 "schedule_interval_seconds": report.schedule_interval_seconds,
+                "service_id": service_id,
             }
         )
         job = store.get_backup_job(job["id"])
@@ -43,10 +61,12 @@ def _get_or_create_job(store: SettingsStore, report: BackupReportRequest) -> dic
 @router.post("/report")
 def post_backup_report(
     report: BackupReportRequest,
+    service_id: str | None = None,
     store: SettingsStore = Depends(get_settings_store),
     _auth: str = Depends(require_api_key),
 ) -> BackupRunResponse:
-    job = _get_or_create_job(store, report)
+    resolved_service_id = _resolve_backup_service_id(store, service_id)
+    job = _get_or_create_job(store, report, resolved_service_id)
 
     # Check for duplicate (same job + started_at within 1s)
     existing_runs = store.list_backup_runs(job_id=job["id"], limit=5)
@@ -88,10 +108,12 @@ def post_backup_report(
 @router.post("/report/start")
 def post_backup_start(
     report: BackupReportRequest,
+    service_id: str | None = None,
     store: SettingsStore = Depends(get_settings_store),
     _auth: str = Depends(require_api_key),
 ) -> BackupRunResponse:
-    job = _get_or_create_job(store, report)
+    resolved_service_id = _resolve_backup_service_id(store, service_id)
+    job = _get_or_create_job(store, report, resolved_service_id)
 
     run_data = {
         "job_id": job["id"],