feat: add combined docker+API service widgets for gitea/coolify/immich/n8n/umami/headscale

One new `service` widget type (nested discriminated union on `service`)
rather than six, so a single config entry shows both docker container
health and a service-specific stat (repo count, project list, photo
count, workflow count, active users, users/nodes) - avoiding the
overhead of configuring a docker widget and a separate service widget
per container. All six collectors hit the service's container name +
internal port directly on falcon_network, the same container-to-
container pattern just proven out for Traefik's own API, avoiding
vpn-only/hairpin-NAT entirely.

Also adds the public/private config split that was scoped in the
original project plan but never built: lib/config/public.ts strips
apiToken/apiKey/password fields before the config reaches the browser
via SSR or the WS config topic - required before any widget could
carry a real secret. Verified via a throwaway secret field that it's
absent from both the SSR HTML and the WS config:update frame.

Endpoint shapes verified live against the running gitea/coolify/immich/
n8n/umami/headscale containers before committing (unauthenticated
requests correctly 401/200 on every target route; gitea's
X-Total-Count header confirmed present).

components/widgets/registry.ts

@@ -7,6 +7,7 @@ import { DatabaseWidget } from "./database/Widget";
 import { SystemWidget } from "./system/Widget";
 import { HttpWidget } from "./http/Widget";
 import { TraefikWidget } from "./traefik/Widget";
+import { ServiceWidget } from "./service/Widget";
 
 type WidgetComponent<T extends Widget["type"]> = ComponentType<{
   widget: Extract<Widget, { type: T }>;
@@ -21,4 +22,5 @@ export const widgetRegistry: { [K in Widget["type"]]: WidgetComponent<K> } = {
   system: SystemWidget,
   http: HttpWidget,
   traefik: TraefikWidget,
+  service: ServiceWidget,
 };