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/hooks/useWidgets.ts

@@ -2,10 +2,9 @@ import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
 import {
 	createWidgetInstance,
 	deleteWidgetInstance,
+	fetchBuiltinWidgetKinds,
 	fetchWidgetData,
 	fetchWidgetInstances,
-	fetchWidgetSources,
-	fetchWidgetTypes,
 	updateWidgetInstance,
 } from "../api/widgets";
 import type { WidgetInstanceInput } from "../types";
@@ -49,16 +48,10 @@ export function useDeleteWidgetInstance() {
 	});
 }
 
-export function useWidgetSources() {
+export function useBuiltinWidgetKinds() {
 	return useQuery({
-		queryKey: ["widgets", "sources"],
-		queryFn: fetchWidgetSources,
-	});
-}
-
-export function useWidgetTypes() {
-	return useQuery({
-		queryKey: ["widgets", "types"],
-		queryFn: fetchWidgetTypes,
+		queryKey: ["widgets", "builtin"],
+		queryFn: fetchBuiltinWidgetKinds,
+		staleTime: 5 * 60 * 1000,
 	});
 }