refactor: 调整项目结构为单向依赖

backend/internal/server/middleware/admin_only.go

@@ -1,7 +1,7 @@
 package middleware
 
 import (
-	"github.com/Wei-Shaw/sub2api/internal/model"
+	"github.com/Wei-Shaw/sub2api/internal/service"
 
 	"github.com/gin-gonic/gin"
 )
@@ -10,15 +10,14 @@ import (
 // 必须在JWTAuth中间件之后使用
 func AdminOnly() gin.HandlerFunc {
 	return func(c *gin.Context) {
-		// 从上下文获取用户
-		user, exists := GetUserFromContext(c)
-		if !exists {
+		role, ok := GetUserRoleFromContext(c)
+		if !ok {
 			AbortWithError(c, 401, "UNAUTHORIZED", "User not found in context")
 			return
 		}
 
 		// 检查是否为管理员
-		if user.Role != model.RoleAdmin {
+		if role != service.RoleAdmin {
 			AbortWithError(c, 403, "FORBIDDEN", "Admin access required")
 			return
 		}