feat(vip): implement layered membership expiry flow

src/Content/VipServiceMembership.php

@@ -27,7 +27,7 @@ trait VipServiceMembership {
         if ($user_id <= 0 || !get_userdata($user_id)) {
             return new \WP_Error('aksrt_vip_user_missing', __('用户不存在。', 'aksrt'));
         }
-        if (!in_array($operation, ['set', 'extend', 'disable'], true)) {
+        if (!in_array($operation, ['set', 'extend', 'disable', 'restore'], true)) {
             return new \WP_Error('aksrt_vip_operation_invalid', __('会员操作无效。', 'aksrt'));
         }
         $reason = sanitize_text_field((string) ($context['reason'] ?? ''));
@@ -97,6 +97,14 @@ trait VipServiceMembership {
 
     /** @param array<string,mixed> $before @param array<string,mixed> $payload @return array{level:int,expires:int}|\WP_Error */
     private function membership_target(array $before, string $operation, array $payload): array|\WP_Error {
+        if ($operation === 'restore') {
+            $level = max(0, min(2, (int) $before['base_level']));
+            $expires = max(0, (int) $before['base_expires']);
+            if ($level <= 0 || ($expires > 0 && $expires <= time())) {
+                return new \WP_Error('aksrt_vip_restore_unavailable', __('没有有效的回退会员可恢复。', 'aksrt'));
+            }
+            return ['level' => $level, 'expires' => $expires];
+        }
         if ($operation === 'disable') {
             return ['level' => 0, 'expires' => 0];
         }