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/api/v1/practice_room.py

@@ -48,6 +48,13 @@ class JoinRoomRequest(BaseModel):
 class SendMessageRequest(BaseModel):
     """发送消息请求"""
     content: str = Field(..., description="消息内容")
+    source: Optional[str] = Field("text", description="消息来源: text/voice")
+
+
+class WebRTCSignalRequest(BaseModel):
+    """WebRTC 信令请求"""
+    signal_type: str = Field(..., description="信令类型: voice_offer/voice_answer/ice_candidate/voice_start/voice_end")
+    payload: dict = Field(..., description="信令数据（SDP/ICE候选等）")
 
 
 class RoomResponse(BaseModel):
@@ -399,6 +406,60 @@ async def send_message(
     }
 
 
+@router.post("/{room_code}/signal", summary="发送WebRTC信令")
+async def send_signal(
+    room_code: str,
+    request: WebRTCSignalRequest,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    """
+    发送 WebRTC 信令消息
+    
+    信令类型：
+    - voice_start: 发起语音通话
+    - voice_offer: SDP Offer
+    - voice_answer: SDP Answer
+    - ice_candidate: ICE 候选
+    - voice_end: 结束语音通话
+    """
+    service = PracticeRoomService(db)
+    
+    # 获取房间
+    room = await service.get_room_by_code(room_code.upper())
+    if not room:
+        raise HTTPException(status_code=404, detail="房间不存在")
+    
+    # 检查用户是否在房间中
+    user_role = room.get_user_role(current_user.id)
+    if not user_role:
+        raise HTTPException(status_code=403, detail="您不是房间参与者")
+    
+    # 验证信令类型
+    valid_signal_types = ["voice_start", "voice_offer", "voice_answer", "ice_candidate", "voice_end"]
+    if request.signal_type not in valid_signal_types:
+        raise HTTPException(status_code=400, detail=f"无效的信令类型，必须是: {', '.join(valid_signal_types)}")
+    
+    # 发送信令消息（作为系统消息存储，用于 SSE 推送）
+    message = await service.send_message(
+        room_id=room.id,
+        user_id=current_user.id,
+        content=None,  # 信令消息不需要文本内容
+        role_name=None,
+        message_type=request.signal_type,
+        extra_data=request.payload
+    )
+    
+    return {
+        "code": 200,
+        "message": "信令发送成功",
+        "data": {
+            "signal_type": request.signal_type,
+            "sequence": message.sequence
+        }
+    }
+
+
 @router.get("/{room_code}/messages", summary="获取消息列表")
 async def get_messages(
     room_code: str,

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)