feat(backend): 在线购买/续费对接 pay 收款中枢——下单/webhook 验签入账/续期叠加/查单兜底

- POST /license/purchase（仅管理员）建单并调 pay 下单，返回收银台 pay_url
- POST /pay/callback 公开接收器：HMAC 验签+时间戳窗口+按 out_trade_no 幂等+金额逐分核对，同事务续期
- 续期与兑换券同口径：未过期从到期日叠加、已过期从现在起算，写入 tier/max_devices/features
- 后台每 60s 查单兜底防 webhook 丢失；closed 标 failed
- 新表 license_purchases（schema.sql/AutoMigrate/testutil 同步）；配置 PAY_SECRET/PAY_BASE_URL/PAY_RETURN_URL
- 契约真相源 ~/code/pay-contract openapi.yaml v1.0.0

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JJ1g8XV1YhhmHRzhwWEW7o

backend/schema/schema.sql

@@ -157,6 +157,31 @@ CREATE TABLE IF NOT EXISTS `license_codes` (
   KEY `idx_redeemed_shop` (`redeemed_shop_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='兑换券码池';
 
+-- ------------------------------------------------------------
+-- 在线购买/续费记录（pay 收款中枢，契约 pay-contract v1.0.0）
+-- out_trade_no = pay 订单号，对账键 + 幂等键；amount 为 pay 回传权威金额
+-- ------------------------------------------------------------
+CREATE TABLE IF NOT EXISTS `license_purchases` (
+  `id`               BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
+  `shop_id`          BIGINT UNSIGNED NOT NULL,
+  `user_id`          BIGINT UNSIGNED NOT NULL COMMENT '下单管理员',
+  `product_biz_code` VARCHAR(64)     NOT NULL COMMENT '套餐稳定码(monthly_standard/annual_standard/monthly_pro/annual_pro)',
+  `amount`           VARCHAR(16)     DEFAULT NULL COMMENT 'pay 下单回传金额，如 2999.00',
+  `out_trade_no`     VARCHAR(64)     DEFAULT NULL COMMENT 'pay 订单号',
+  `status`           ENUM('pending','paid','failed') NOT NULL DEFAULT 'pending',
+  `trade_no`         VARCHAR(64)     DEFAULT NULL COMMENT '渠道交易号(支付宝/微信)',
+  `channel`          VARCHAR(16)     DEFAULT NULL,
+  `paid_at`          DATETIME        DEFAULT NULL,
+  `created_at`       DATETIME        NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  `updated_at`       DATETIME        NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+  `deleted_at`       DATETIME        DEFAULT NULL,
+  PRIMARY KEY (`id`),
+  UNIQUE KEY `uk_out_trade_no` (`out_trade_no`),
+  KEY `idx_shop` (`shop_id`),
+  KEY `idx_status` (`status`),
+  KEY `idx_deleted_at` (`deleted_at`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='在线购买/续费记录';
+
 -- ------------------------------------------------------------
 -- 商品分类
 -- ------------------------------------------------------------