feat: unify invite flow with referral ref

src/Credits/Credits.php

@@ -33,8 +33,8 @@ class Credits {
      *
      * @param int    $user_id
      * @param int    $delta   必须 > 0
-     * @param string $reason  例 register/signin/comment/invite/admin
-     * @param array  $ref     ['type' => 'post|comment|user|invite', 'id' => int]
+     * @param string $reason  例 register/signin/comment/referral/admin
+     * @param array  $ref     ['type' => 'post|comment|user|referral', 'id' => int]
      * @return int|\WP_Error 新余额或错误
      */
     public static function add(int $user_id, int $delta, string $reason, array $ref = [], string $remark = '', bool $dispatch_hooks = true) {