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/widgets/index.ts

@@ -4,9 +4,3 @@ export { JellyfinWidget } from "./JellyfinWidget";
 export { PrometheusMetricWidget } from "./PrometheusMetricWidget";
 export { SshTaskWidget } from "./SshTaskWidget";
 export { StaticWidget } from "./StaticWidget";
-export {
-	getWidgetDefinition,
-	listWidgetTypes,
-	WIDGET_REGISTRY,
-} from "./registry";
-export type { WidgetConfigField, WidgetDefinition } from "./registry";