feat(invite-code): one-time invite codes with rewards, usage log, import/export

- 一次性邀请码：批量生成（次数/有效期/备注/四类奖励）、原子消费防超发、
  开启注册验证时奖励延迟发放（账本幂等键）
- Zibll 兼容文本导入（points/balance/vip/vip_time/level_integral，分隔符可自定义，
  第三段标识存为备注）、CSV 全字段导出与可回流文本导出
- 使用记录表 aksrt_invite_code_usage + 后台使用者列；注册表单 400ms 防抖实时校验
- 注册门控三模式（close/open/must）设置链路（PHP schema + admin SPA schema）
- 契约测试覆盖建表/消费竞态/导入导出/备注全链路

src/Auth/ServicePart1b.php

@@ -96,12 +96,33 @@ trait ServicePart1b {
 			return ['success' => false, 'error' => __('推广码无效，请检查后重试', 'aksrt')];
 		}
 
+		$invite_service = class_exists('\AKSRT\Payment\InviteCode')
+			? \AKSRT\Payment\InviteCode::get_instance()
+			: null;
+		if ($invite_service) {
+			$invite_service->clear_registration_context();
+			$invite_mode = $invite_service->field_mode();
+			$submitted_invite = sanitize_key((string) ($post['invite_code'] ?? ''));
+			if ($invite_mode === 'required' && $submitted_invite === '') {
+				return ['success' => false, 'error' => __('请填写邀请码', 'aksrt')];
+			}
+			if ($submitted_invite !== '') {
+				if (!$invite_service->is_valid($submitted_invite)) {
+					return ['success' => false, 'error' => __('邀请码无效或已用完，请检查后重试', 'aksrt')];
+				}
+				$invite_service->set_registration_context($submitted_invite);
+			}
+		}
+
 		// 创建用户
 		$user_id = wp_create_user($username, $pass, '');
 		if (is_wp_error($user_id)) {
 			if ($ref_service) {
 				$ref_service->clear_registration_context();
 			}
+			if ($invite_service) {
+				$invite_service->clear_registration_context();
+			}
 			return ['success' => false, 'error' => $user_id->get_error_message()];
 		}