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).

app/page.tsx

@@ -1,5 +1,6 @@
 import { ConfigError } from "@/lib/config/loader";
 import { effectiveConfigStore } from "@/lib/config/effective";
+import { toPublicConfig } from "@/lib/config/public";
 import { Dashboard } from "@/components/layout/Dashboard";
 
 export const dynamic = "force-dynamic";
@@ -20,5 +21,5 @@ export default function Home() {
     );
   }
 
-  return <Dashboard config={config} />;
+  return <Dashboard config={toPublicConfig(config)} />;
 }