fix(frontend): Fix SignalR 401 authentication error with dynamic token factory

Fixed SignalR connection failing with 401 Unauthorized error by using
a dynamic token factory instead of a static token value.

Changes:
- Updated accessTokenFactory to call tokenManager.getAccessToken() dynamically
- This ensures SignalR always uses the latest valid JWT token
- Fixes token expiration and refresh issues during connection lifecycle

Issue: SignalR negotiation was failing because it used a stale token
captured at connection creation time, instead of fetching the current
token from localStorage on each request.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/signalr/ConnectionManager.ts

@@ -36,7 +36,8 @@ export class SignalRConnectionManager {
 
     this.connection = new signalR.HubConnectionBuilder()
       .withUrl(this.hubUrl, {
-        accessTokenFactory: () => token,
+        // Use dynamic token factory to always get the latest token
+        accessTokenFactory: () => tokenManager.getAccessToken() || '',
         // 备用方案：使用 query string（WebSocket 升级需要）
         // transport: signalR.HttpTransportType.WebSockets,
       })