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/index.html

@@ -17,7 +17,8 @@
           Use the desktop client to sign in, provision this device, and connect to your private network.
         </p>
         <div class="actions">
-          <a class="button primary" href="/api/v1/healthz">API health</a>
+          <a class="button primary" href="/status">System status</a>
+          <a class="button secondary" href="/api/v1/status">Raw API status</a>
         </div>
       </section>