feat(diagnosis): add streaming progress support and tunnel-grouped forward list

- Add SSE streaming endpoints for tunnel/forward diagnosis with real-time progress
- Increase diagnosis timeout to 2 minutes with context propagation
- Group forwards by tunnel within user groups in UI
- Add nginx SSE proxy configuration for streaming endpoints

go-backend/internal/app/app.go

@@ -49,7 +49,7 @@ func New(cfg config.Config) (*App, error) {
 		Handler:           router,
 		ReadTimeout:       30 * time.Second,
 		ReadHeaderTimeout: 5 * time.Second,
-		WriteTimeout:      30 * time.Second,
+		WriteTimeout:      2 * time.Minute,
 		IdleTimeout:       60 * time.Second,
 	}