fix(api): reject invalid UUID variants

backend/internal/httpx/params.go

@@ -10,7 +10,7 @@ import (
 // IdentityParam 只接受 UUIDv7 路径参数，避免把内部自增 ID 暴露为外部标识。
 func IdentityParam(c *gin.Context, name string) (string, bool) {
 	identity, err := uuid.Parse(c.Param(name))
-	if err != nil || identity.Version() != 7 {
+	if err != nil || identity.Version() != 7 || identity.Variant() != uuid.RFC4122 {
 		Error(c, http.StatusBadRequest, "invalid_request", "请求参数无效")
 		return "", false
 	}