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).

lib/collectors/services/base-url.ts

@@ -0,0 +1,14 @@
+import type { ServiceWidget } from "@/lib/config/schema";
+
+const SERVICE_PORTS: Record<ServiceWidget["service"], number> = {
+  gitea: 3000,
+  coolify: 8080,
+  immich: 2283,
+  n8n: 5678,
+  umami: 3000,
+  headscale: 8080,
+};
+
+export function serviceBaseUrl(widget: ServiceWidget): string {
+  return `http://${widget.containerName}:${SERVICE_PORTS[widget.service]}`;
+}