chore: 删除未使用的孤立包

清理以下未导入的包:
- internal/response (未使用的响应结构体)
- pkg/response (未使用的响应封装)
- internal/model (TLSFingerprintProfile, ErrorPassthroughRule)
- internal/models (SocialAccount, domain已有)
- internal/pkg/response (未使用的响应封装)
- internal/security/ratelimit (已迁移到middleware)

验证: go build ./... && go test ./... 通过

pkg/response/response.go

@@ -1,50 +0,0 @@
-package response
-
-import (
-	"net/http"
-
-	"github.com/gin-gonic/gin"
-)
-
-// Response 统一响应结构
-type Response struct {
-	Code    int         `json:"code"`
-	Message string      `json:"message"`
-	Data    interface{} `json:"data,omitempty"`
-}
-
-// Success 成功响应
-func Success(c *gin.Context, data interface{}) {
-	c.JSON(http.StatusOK, Response{
-		Code:    0,
-		Message: "success",
-		Data:    data,
-	})
-}
-
-// Error 错误响应
-func Error(c *gin.Context, httpStatus int, message string, err error) {
-	if err != nil {
-		// 在开发环境下返回详细错误信息
-		if gin.Mode() == gin.DebugMode {
-			c.JSON(httpStatus, Response{
-				Code:    httpStatus,
-				Message: message,
-				Data:    err.Error(),
-			})
-			return
-		}
-	}
-	c.JSON(httpStatus, Response{
-		Code:    httpStatus,
-		Message: message,
-	})
-}
-
-// ErrorWithCode 错误响应（带自定义错误码）
-func ErrorWithCode(c *gin.Context, code int, message string) {
-	c.JSON(http.StatusOK, Response{
-		Code:    code,
-		Message: message,
-	})
-}