修复(#71): 管理员订阅限速接口拒绝负数限速和非法 traffic_limit

- SpeedLimit 加 validate:"gte=0" 校验
- TrafficLimit 加 JSON 格式校验
- 新增单测覆盖负数限速和非法 JSON 场景

Co-authored-by: multica-agent <github@multica.ai>

internal/handler/admin/user/updateUserSubscribeHandler.go

@@ -1,6 +1,9 @@
 package user
 
 import (
+	"encoding/json"
+	"errors"
+
 	"github.com/gin-gonic/gin"
 	"github.com/perfect-panel/server/internal/logic/admin/user"
 	"github.com/perfect-panel/server/internal/svc"
@@ -18,9 +21,25 @@ func UpdateUserSubscribeHandler(svcCtx *svc.ServiceContext) func(c *gin.Context)
 			result.ParamErrorResult(c, validateErr)
 			return
 		}
+		if err := validateUpdateUserSubscribeTrafficLimit(&req); err != nil {
+			result.ParamErrorResult(c, err)
+			return
+		}
 
 		l := user.NewUpdateUserSubscribeLogic(c.Request.Context(), svcCtx)
 		err := l.UpdateUserSubscribe(&req)
 		result.HttpResult(c, nil, err)
 	}
 }
+
+func validateUpdateUserSubscribeTrafficLimit(req *types.UpdateUserSubscribeRequest) error {
+	if req.TrafficLimit == nil || *req.TrafficLimit == "" {
+		return nil
+	}
+
+	var rules []types.TrafficLimit
+	if err := json.Unmarshal([]byte(*req.TrafficLimit), &rules); err != nil {
+		return errors.New("traffic_limit must be a valid JSON array")
+	}
+	return nil
+}