fix: use connection.socket for @fastify/websocket v8

backend/src/plugins/websocket.ts

@@ -13,7 +13,7 @@ interface AlertMessage {
     timestamp: string;
 }
 
-// Connected clients (using any to avoid ws type issues)
+// Connected clients (storing the raw WebSocket)
 const clients: Map<string, any> = new Map();
 
 export async function websocketPlugin(fastify: FastifyInstance) {
@@ -22,9 +22,12 @@ export async function websocketPlugin(fastify: FastifyInstance) {
     /**
      * WebSocket endpoint for real-time alerts
      */
-    fastify.get('/ws/alerts', { websocket: true }, (socket, request) => {
+    fastify.get('/ws/alerts', { websocket: true }, (connection, request) => {
         const clientId = `${Date.now()}-${Math.random().toString(36).slice(2)}`;
 
+        // Get the raw WebSocket from the SocketStream
+        const socket = connection.socket;
+
         clients.set(clientId, socket);
         fastify.log.info(`WebSocket client connected: ${clientId}`);