feat: 医生端Web后台 + SignalR实时问诊

- 新增 doctor_web/ React前端 (dashboard/患者/问诊/报告/随访)
- 后端新增 doctor_endpoints (14个医生API) + ConsultationHub (SignalR)
- Flutter端 SignalR 替换轮询实现实时聊天

health_app/lib/pages/consultation/consultation_pages.dart

@@ -103,7 +103,7 @@ class _DoctorChatPageState extends ConsumerState<DoctorChatPage> {
 
   @override
   void dispose() {
-    ref.read(consultationChatProvider.notifier).stopPolling();
+    ref.read(consultationChatProvider.notifier).stop();
     _textCtrl.dispose();
     _scrollCtrl.dispose();
     super.dispose();