feat: 添加双人对练语音通话功能

- 后端：扩展 SSE 支持 WebRTC 信令消息转发
- 前端：创建 WebRTC 连接管理模块 (webrtc.ts)
- 前端：创建 useVoiceCall 组合式函数
- 前端：在对练房间添加语音通话 UI
- 集成 Web Speech API 实现语音转文字

backend/app/services/practice_room_service.py

@@ -271,44 +271,56 @@ class PracticeRoomService:
         self,
         room_id: int,
         user_id: int,
-        content: str,
-        role_name: Optional[str] = None
+        content: Optional[str],
+        role_name: Optional[str] = None,
+        message_type: Optional[str] = None,
+        extra_data: Optional[dict] = None
     ) -> PracticeRoomMessage:
         """
-        发送聊天消息
+        发送聊天消息或信令消息
         
         Args:
             room_id: 房间ID
             user_id: 发送者ID
             content: 消息内容
             role_name: 角色名称
+            message_type: 消息类型（默认为 chat）
+            extra_data: 额外数据（用于 WebRTC 信令等）
             
         Returns:
             PracticeRoomMessage: 消息对象
         """
+        import json
+        
         # 获取当前消息序号
         sequence = await self._get_next_sequence(room_id)
         
+        # 如果是信令消息，将 extra_data 序列化到 content 中
+        actual_content = content
+        if extra_data and not content:
+            actual_content = json.dumps(extra_data)
+        
         message = PracticeRoomMessage(
             room_id=room_id,
             user_id=user_id,
-            message_type=self.MSG_TYPE_CHAT,
-            content=content,
+            message_type=message_type or self.MSG_TYPE_CHAT,
+            content=actual_content,
             role_name=role_name,
             sequence=sequence
         )
         
         self.db.add(message)
         
-        # 更新房间统计
-        room = await self.get_room_by_id(room_id)
-        if room:
-            room.total_turns += 1
-            user_role = room.get_user_role(user_id)
-            if user_role == "A":
-                room.role_a_turns += 1
-            elif user_role == "B":
-                room.role_b_turns += 1
+        # 只有聊天消息才更新房间统计
+        if (message_type or self.MSG_TYPE_CHAT) == self.MSG_TYPE_CHAT:
+            room = await self.get_room_by_id(room_id)
+            if room:
+                room.total_turns += 1
+                user_role = room.get_user_role(user_id)
+                if user_role == "A":
+                    room.role_a_turns += 1
+                elif user_role == "B":
+                    room.role_b_turns += 1
         
         await self.db.commit()
         await self.db.refresh(message)