feat: 店铺密码检测任务（后台发起→客户端领取→紫鸟真实登录判定→回传结果）

- 新增 biz_shop_credential_check 表（V99）与 ShopCredentialCheck 全链路
- Controller /api/admin/shop-credential-checks（create/poll/report/latest，X-Internal-Token 鉴权）
- ShopManageService 列表附带 latestCheck（每店铺最近一次检测结果）
- 客户端通过 poll 领取（60s 轮询、原子置 RUNNING），报告 SUCCESS/FAILED/OTP_REQUIRED/NO_NEED_LOGIN/ERROR

backend-java/src/main/resources/db/V99__shop_credential_check.sql

@@ -0,0 +1,16 @@
+CREATE TABLE IF NOT EXISTS `biz_shop_credential_check` (
+    `id` BIGINT NOT NULL AUTO_INCREMENT,
+    `shop_id` BIGINT NOT NULL,
+    `shop_name` VARCHAR(255) NOT NULL,
+    `status` VARCHAR(32) NOT NULL DEFAULT 'PENDING',
+    `detail` VARCHAR(1024) NULL,
+    `client_host` VARCHAR(255) NULL,
+    `try_requested_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    `check_started_at` DATETIME NULL,
+    `check_finished_at` DATETIME NULL,
+    `created_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    `updated_at` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+    PRIMARY KEY (`id`),
+    KEY `idx_shop_credential_check_shop_status` (`shop_id`, `status`, `id`),
+    KEY `idx_shop_credential_check_status_id` (`status`, `id`)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;