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/Dashboard.tsx

@@ -30,7 +30,7 @@ import type { DashboardShortcut, DashboardShortcutInput } from "../types";
 import { SectionCard } from "../components/SectionCard";
 import { ConfirmDialog } from "../components/ConfirmDialog";
 import { DialogFooter } from "../components/DialogFooter";
-import { WidgetInstance } from "../components/WidgetInstance";
+import { WidgetInstanceCard } from "../components/WidgetInstance";
 import { WidgetConfigDialog } from "../components/WidgetConfigDialog";
 
 function emptyShortcut(): DashboardShortcutInput {
@@ -418,7 +418,7 @@ export function Dashboard() {
 			</SectionCard>
 
 			{visibleWidgets.map((widget) => (
-				<WidgetInstance key={widget.id} widget={widget} />
+				<WidgetInstanceCard key={widget.id} widget={widget} />
 			))}
 
 			<ShortcutDialog