mcp-hub-002: WebSocket backend registration and health tracking

src/server.js

@@ -1,4 +1,5 @@
 const express = require('express');
+const registry = require('./backend-registry');
 
 const app = express();
 
@@ -16,7 +17,7 @@ app.get('/health', (req, res) => {
   res.json({
     status: 'ok',
     uptime: process.uptime(),
-    connectedBackends: 0,
+    connectedBackends: registry.count(),
   });
 });