feat: add public status page with component health monitoring and system metrics visualization

Add statuspage package with service, handler, and types for exposing platform health. Implement GET /api/v1/status endpoint returning operational status, component health (API, database, gateway runtime), and control plane summary counts.

Add Service.Snapshot method querying database connectivity, user/device/gateway/service/policy counts, connected device count via handshake timestamps, and gateway runtime tel

public-web/nginx.conf

@@ -12,6 +12,10 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
     }
 
+    location = /status {
+        try_files /status.html =404;
+    }
+
     location / {
         try_files $uri /index.html;
     }