feat: 初始化 Go 后端项目骨架

- 使用 Gin 框架替代原始 net/http，方便调试
- 实现 WebSocket 端点 (/ws)，支持 ping/query/config/interrupt 消息
- 实现健康检查 REST 接口 (/api/health)
- 定义协议数据结构 (models)
- 心跳检测（60 秒超时断开）

backend/internal/ws/handler.go

@@ -0,0 +1,149 @@
+package ws
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+	"github.com/gorilla/websocket"
+
+	"github.com/hhs/camtalk/internal/models"
+)
+
+var upgrader = websocket.Upgrader{
+	CheckOrigin: func(r *http.Request) bool { return true }, // 开发阶段允许所有来源
+}
+
+// Client 代表一个 WebSocket 客户端连接。
+type Client struct {
+	conn      *websocket.Conn
+	sessionID string
+	mu        sync.Mutex
+}
+
+func (c *Client) sendJSON(v any) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.conn.WriteJSON(v)
+}
+
+// ServeWS 处理 WebSocket 升级请求。
+func ServeWS(c *gin.Context) {
+	conn, err := upgrader.Upgrade(c.Writer, c.Request, nil)
+	if err != nil {
+		log.Printf("websocket upgrade failed: %v", err)
+		return
+	}
+	defer conn.Close()
+
+	sessionID := uuid.New().String()
+	client := &Client{conn: conn, sessionID: sessionID}
+
+	// 发送 connected 消息
+	_ = client.sendJSON(models.WsConnected{
+		Type:          "connected",
+		SessionID:     sessionID,
+		ServerVersion: "0.1.0",
+	})
+	log.Printf("client connected: session=%s", sessionID)
+
+	// 心跳检测
+	lastPong := time.Now()
+	conn.SetPongHandler(func(string) error {
+		lastPong = time.Now()
+		return nil
+	})
+
+	// 启动心跳检查 goroutine
+	done := make(chan struct{})
+	go func() {
+		ticker := time.NewTicker(30 * time.Second)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				if time.Since(lastPong) > 60*time.Second {
+					log.Printf("heartbeat timeout: session=%s", sessionID)
+					conn.Close()
+					return
+				}
+			case <-done:
+				return
+			}
+		}
+	}()
+
+	// 消息读取循环
+	for {
+		_, message, err := conn.ReadMessage()
+		if err != nil {
+			if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseNormalClosure) {
+				log.Printf("ws read error: %v", err)
+			}
+			break
+		}
+
+		// 解析消息类型
+		var envelope struct {
+			Type string `json:"type"`
+		}
+		if err := json.Unmarshal(message, &envelope); err != nil {
+			_ = client.sendJSON(models.WsError{
+				Type:    "error",
+				Code:    "INVALID_MESSAGE",
+				Message: "invalid JSON",
+			})
+			continue
+		}
+
+		switch envelope.Type {
+		case "ping":
+			_ = client.sendJSON(models.WsPong{Type: "pong"})
+
+		case "query":
+			var msg models.WsQuery
+			if err := json.Unmarshal(message, &msg); err != nil {
+				_ = client.sendJSON(models.WsError{
+					Type:      "error",
+					Code:      "INVALID_MESSAGE",
+					Message:   "invalid query message",
+					RequestID: msg.RequestID,
+				})
+				continue
+			}
+			log.Printf("query received: session=%s request=%s", sessionID, msg.RequestID)
+			// TODO: 调用 AI 编排流程（STT → LLM → TTS）
+
+		case "config":
+			var msg models.WsConfig
+			if err := json.Unmarshal(message, &msg); err != nil {
+				_ = client.sendJSON(models.WsError{
+					Type:    "error",
+					Code:    "INVALID_MESSAGE",
+					Message: "invalid config message",
+				})
+				continue
+			}
+			log.Printf("config update: session=%s", sessionID)
+			// TODO: 更新会话配置
+
+		case "interrupt":
+			log.Printf("interrupt received: session=%s", sessionID)
+			// TODO: 中断当前 AI 响应
+
+		default:
+			_ = client.sendJSON(models.WsError{
+				Type:    "error",
+				Code:    "INVALID_MESSAGE",
+				Message: "unknown message type: " + envelope.Type,
+			})
+		}
+	}
+
+	close(done)
+	log.Printf("client disconnected: session=%s", sessionID)
+}