feat(services): frontend services runtime and widget rebind

PR 3 of 4 for the runtime service registry change.

- Add service + new-shape widget TypeScript types; widgets carry service_id
  + widget_kind (service-bound) or null (built-in).
- Add services API client + TanStack Query hooks; reconcile the widget API
  client/hooks to the new endpoints (remove sources/types; add builtin kinds).
- Add closed frontend service registry (integrations/registry.ts) mirroring the
  backend, with resolveWidget(widget, services) mapping a widget to its
  component + refresh interval.
- Add ServicePage at /services/:serviceType/:serviceId with config view,
  empty-on-edit secret inputs + 'set' badges, enable toggle, delete, and the
  service's widget-kind list.
- Register /services/:serviceType/:serviceId in App.tsx.
- Reconcile the six widget components to refreshIntervalMs + description props;
  rewrite WidgetConfigDialog around a service -> widget-kind picker.
- Update Dashboard test; add integrations/registry.test.ts.

Verification: frontend lint 0 errors, build success, 70 tests passed; backend
ruff clean, 222 tests passed.

frontend/src/pages/__tests__/Dashboard.test.tsx

@@ -5,12 +5,12 @@ import { Dashboard } from "../Dashboard";
 import type { DashboardShortcut } from "../../types";
 
 // Stub the composed widgets so the test exercises Dashboard's own behavior
-// (shortcut CRUD) without rendering the session panel or the backup query.
-vi.mock("../../components/NowPlaying", () => ({
-	NowPlaying: () => <div data-testid="now-playing-stub" />,
+// (shortcut CRUD) without rendering widgets or their data queries.
+vi.mock("../../components/WidgetInstance", () => ({
+	WidgetInstanceCard: () => <div data-testid="widget-stub" />,
 }));
-vi.mock("../../components/BackupDashboardWidget", () => ({
-	default: () => <div data-testid="backup-widget-stub" />,
+vi.mock("../../components/WidgetConfigDialog", () => ({
+	WidgetConfigDialog: () => <div data-testid="widget-config-stub" />,
 }));
 
 const navigate = vi.fn();
@@ -21,6 +21,9 @@ vi.mock("react-router-dom", () => ({
 vi.mock("../../hooks/useSettings", () => ({
 	useMonitoringSettings: () => ({ data: [] }),
 }));
+vi.mock("../../hooks/useWidgets", () => ({
+	useWidgetInstances: () => ({ data: [] }),
+}));
 
 const saveShortcutMutate = vi.fn().mockResolvedValue({});
 const deleteShortcutMutate = vi.fn();