fix: call closeAllConnections() before server.close()

server.close() only stops accepting new connections but does not
terminate existing keep-alive connections. This can cause the cleanup
promise to hang indefinitely in test suites or production.

Add server.closeAllConnections() (Node.js 18.2+) before server.close()
in both single-account and bulk cleanup paths.

Addresses greptile review feedback.

extensions/feishu/src/monitor.state.ts

@@ -137,6 +137,7 @@ export function stopFeishuMonitorState(accountId?: string): void {
     wsClients.delete(accountId);
     const server = httpServers.get(accountId);
     if (server) {
+      server.closeAllConnections();
       server.close();
       httpServers.delete(accountId);
     }
@@ -147,6 +148,7 @@ export function stopFeishuMonitorState(accountId?: string): void {
 
   wsClients.clear();
   for (const server of httpServers.values()) {
+    server.closeAllConnections();
     server.close();
   }
   httpServers.clear();