feat(auth): add Casbin RBAC and user activity tracking

Integrate Casbin for role-based access control with admin routes for role management. Add user activity logging service to track login and refresh events. Refactor audit service to use AI-based content moderation.

internal/errors/app_errors.go

@@ -90,6 +90,15 @@ var (
 
 	// 通知相关错误
 	ErrUnauthorizedNotification = &AppError{Code: "UNAUTHORIZED_NOTIFICATION", Message: "无权删除此通知"}
+
+	// Casbin 相关错误
+	ErrPermissionDenied       = &AppError{Code: "PERMISSION_DENIED", Message: "权限不足"}
+	ErrRoleNotFound           = &AppError{Code: "ROLE_NOT_FOUND", Message: "角色不存在"}
+	ErrRoleAlreadyAssigned    = &AppError{Code: "ROLE_ALREADY_ASSIGNED", Message: "用户已拥有该角色"}
+	ErrRoleNotAssigned        = &AppError{Code: "ROLE_NOT_ASSIGNED", Message: "用户未拥有该角色"}
+	ErrCannotModifyOwnRole    = &AppError{Code: "CANNOT_MODIFY_OWN_ROLE", Message: "不能修改自己的角色"}
+	ErrCannotModifySuperAdmin = &AppError{Code: "CANNOT_MODIFY_SUPER_ADMIN", Message: "不能修改超级管理员角色"}
+	ErrCasbinInternal         = &AppError{Code: "CASBIN_INTERNAL_ERROR", Message: "权限系统内部错误"}
 )
 
 // Wrap 包装错误