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/components/WidgetInstance.tsx

@@ -1,5 +1,6 @@
 import { Alert, AlertDescription } from "@/components/ui/alert";
-import { getWidgetDefinition } from "../widgets/registry";
+import { useServiceInstances } from "../hooks/useServices";
+import { resolveWidget } from "../integrations/registry";
 import type { WidgetInstance } from "../types";
 import { SectionCard } from "./SectionCard";
 
@@ -7,20 +8,29 @@ interface Props {
 	widget: WidgetInstance;
 }
 
-export function WidgetInstance({ widget }: Props) {
-	const def = getWidgetDefinition(widget.widget_type);
-	if (!def) {
+export function WidgetInstanceCard({ widget }: Props) {
+	const { data: services = [] } = useServiceInstances();
+	const resolved = resolveWidget(widget, services);
+
+	if (!resolved) {
+		const label = widget.service_id
+			? `Unknown widget: ${widget.widget_kind} (service-bound)`
+			: `Unknown widget: ${widget.widget_kind} (built-in)`;
 		return (
 			<SectionCard title={widget.title}>
 				<Alert>
-					<AlertDescription>
-						Unknown widget type: {widget.widget_type}
-					</AlertDescription>
+					<AlertDescription>{label}</AlertDescription>
 				</Alert>
 			</SectionCard>
 		);
 	}
 
-	const Component = def.component;
-	return <Component widget={widget} />;
+	const Component = resolved.component;
+	return (
+		<Component
+			widget={widget}
+			refreshIntervalMs={resolved.refreshIntervalMs}
+			description={resolved.description}
+		/>
+	);
 }