feat: main.go 接入配置 + graceful shutdown + logger 迁移

- main.go: 接入 config.Load() 替换硬编码 :8080
- main.go: 添加 signal.NotifyContext + http.Server.Shutdown（10s drain）
- main.go: 初始化 Zap 日志，prod 环境切换 Gin release 模式
- ws/handler.go: 所有 log.Printf 替换为 logger.Log 结构化日志
- 修复 .gitignore 排除规则（/server 仅匹配根目录二进制）
- 新增 zap、viper 依赖

backend/internal/ws/handler.go

@@ -2,7 +2,6 @@ package ws
 
 import (
 	"encoding/json"
-	"log"
 	"net/http"
 	"sync"
 	"time"
@@ -11,6 +10,7 @@ import (
 	"github.com/google/uuid"
 	"github.com/gorilla/websocket"
 
+	"github.com/hhs/camtalk/internal/logger"
 	"github.com/hhs/camtalk/internal/models"
 )
 
@@ -35,7 +35,7 @@ func (c *Client) sendJSON(v any) error {
 func ServeWS(c *gin.Context) {
 	conn, err := upgrader.Upgrade(c.Writer, c.Request, nil)
 	if err != nil {
-		log.Printf("websocket upgrade failed: %v", err)
+		logger.Log.Errorw("websocket upgrade failed", "error", err)
 		return
 	}
 	defer conn.Close()
@@ -49,7 +49,7 @@ func ServeWS(c *gin.Context) {
 		SessionID:     sessionID,
 		ServerVersion: "0.1.0",
 	})
-	log.Printf("client connected: session=%s", sessionID)
+	logger.Log.Infow("client connected", "session", sessionID)
 
 	// 心跳检测
 	lastPong := time.Now()
@@ -67,7 +67,7 @@ func ServeWS(c *gin.Context) {
 			select {
 			case <-ticker.C:
 				if time.Since(lastPong) > 60*time.Second {
-					log.Printf("heartbeat timeout: session=%s", sessionID)
+					logger.Log.Warnw("heartbeat timeout", "session", sessionID)
 					conn.Close()
 					return
 				}
@@ -82,7 +82,7 @@ func ServeWS(c *gin.Context) {
 		_, message, err := conn.ReadMessage()
 		if err != nil {
 			if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseNormalClosure) {
-				log.Printf("ws read error: %v", err)
+				logger.Log.Warnw("ws read error", "error", err)
 			}
 			break
 		}
@@ -115,7 +115,7 @@ func ServeWS(c *gin.Context) {
 				})
 				continue
 			}
-			log.Printf("query received: session=%s request=%s", sessionID, msg.RequestID)
+			logger.Log.Infow("query received", "session", sessionID, "request", msg.RequestID)
 			// TODO: 调用 AI 编排流程（STT → LLM → TTS）
 
 		case "config":
@@ -128,11 +128,11 @@ func ServeWS(c *gin.Context) {
 				})
 				continue
 			}
-			log.Printf("config update: session=%s", sessionID)
+			logger.Log.Infow("config update", "session", sessionID)
 			// TODO: 更新会话配置
 
 		case "interrupt":
-			log.Printf("interrupt received: session=%s", sessionID)
+			logger.Log.Infow("interrupt received", "session", sessionID)
 			// TODO: 中断当前 AI 响应
 
 		default:
@@ -145,5 +145,5 @@ func ServeWS(c *gin.Context) {
 	}
 
 	close(done)
-	log.Printf("client disconnected: session=%s", sessionID)
+	logger.Log.Infow("client disconnected", "session", sessionID)
 }