feat: 集成限流器到服务

- main.go 初始化限流器（根据 Redis 可用性选择内存/Redis 实现）
- WebSocket handler 添加 query 消息限流（按 userID）
- Auth API 添加登录/注册限流（按 IP）
- refresh 和 logout 不限流（避免影响正常用户操作）
- 修复所有测试（传递 nil limiter 参数）
- 所有测试通过（包括 ws 和 api 集成测试）

backend/internal/ws/handler.go

@@ -3,6 +3,7 @@ package ws
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/http"
 	"sync"
 	"time"
@@ -17,6 +18,7 @@ import (
 	"github.com/hhs/camtalk/internal/logger"
 	"github.com/hhs/camtalk/internal/models"
 	"github.com/hhs/camtalk/internal/orchestrator"
+	"github.com/hhs/camtalk/internal/ratelimit"
 	"github.com/hhs/camtalk/internal/session"
 )
 
@@ -93,19 +95,19 @@ func (w *WSClient) SendError(err models.WsError) error {
 }
 
 // ServeWS 处理 WebSocket 升级请求。
-func ServeWS(sessionMgr session.Manager, orch orchestrator.Orchestrator, cfg *config.Config, tokenMgr *auth.TokenManager) gin.HandlerFunc {
+func ServeWS(sessionMgr session.Manager, orch orchestrator.Orchestrator, cfg *config.Config, tokenMgr *auth.TokenManager, limiter ratelimit.Limiter) gin.HandlerFunc {
 	upgrader := newUpgrader(cfg)
 	heartbeatInterval := time.Duration(cfg.Server.HeartbeatInterval) * time.Second
 	heartbeatTimeout := time.Duration(cfg.Server.HeartbeatTimeout) * time.Second
 	version := cfg.App.Version
 
 	return func(c *gin.Context) {
-		serveWS(c, sessionMgr, orch, upgrader, heartbeatInterval, heartbeatTimeout, version, tokenMgr)
+		serveWS(c, sessionMgr, orch, upgrader, heartbeatInterval, heartbeatTimeout, version, tokenMgr, limiter)
 	}
 }
 
 func serveWS(c *gin.Context, sessionMgr session.Manager, orch orchestrator.Orchestrator,
-	upgrader websocket.Upgrader, heartbeatInterval, heartbeatTimeout time.Duration, version string, tokenMgr *auth.TokenManager) {
+	upgrader websocket.Upgrader, heartbeatInterval, heartbeatTimeout time.Duration, version string, tokenMgr *auth.TokenManager, limiter ratelimit.Limiter) {
 
 	// --- JWT 认证（upgrade 前完成，失败直接返回 HTTP 错误） ---
 	token := c.Query("token")
@@ -225,6 +227,18 @@ func serveWS(c *gin.Context, sessionMgr session.Manager, orch orchestrator.Orche
 			}
 			logger.Log.Infow("query received", "session", sessionID, "request", msg.RequestID)
 
+			// 限流检查
+			if limiter != nil {
+				key := fmt.Sprintf("%s:query", userID)
+				allowed, retryAfter := limiter.Allow(context.Background(), key)
+				if !allowed {
+					logger.Log.Warnw("rate limited", "user_id", userID, "retry_after", retryAfter)
+					errors.SendWSError(client, errors.CodeRateLimited, msg.RequestID,
+						fmt.Errorf("rate limited, retry after %s", retryAfter.Round(time.Second)))
+					continue
+				}
+			}
+
 			// 刷新会话 TTL
 			if err := client.sessionMgr.Touch(context.Background(), sessionID); err != nil {
 				logger.Log.Warnw("touch session failed", "session", sessionID, "error", err)