feat: add digital employee management sync endpoint

qiming-backend/sql/update-20260605.sql

@@ -0,0 +1,23 @@
+CREATE TABLE `digital_employee_sync_record`
+(
+    `id`          BIGINT       NOT NULL AUTO_INCREMENT COMMENT '主键',
+    `_tenant_id`  BIGINT       DEFAULT NULL COMMENT '租户ID',
+    `user_id`     BIGINT       DEFAULT NULL COMMENT '用户ID',
+    `client_key`  VARCHAR(128) NOT NULL COMMENT '客户端配置Key',
+    `device_id`   VARCHAR(128) DEFAULT NULL COMMENT '设备ID',
+    `outbox_id`   VARCHAR(255) NOT NULL COMMENT '客户端outbox ID',
+    `entity_type` VARCHAR(32)  NOT NULL COMMENT '实体类型：plan/task/run/event/artifact/approval',
+    `entity_id`   VARCHAR(255) NOT NULL COMMENT '客户端实体ID',
+    `operation`   VARCHAR(32)  NOT NULL COMMENT '操作类型',
+    `payload`     JSON         DEFAULT NULL COMMENT '实体快照',
+    `synced_at`   DATETIME     NOT NULL COMMENT '最近同步时间',
+    `modified`    DATETIME     NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+    `created`     DATETIME     NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (`id`),
+    UNIQUE KEY `uk_client_outbox` (`client_key`, `outbox_id`),
+    KEY `idx_client_entity` (`client_key`, `entity_type`, `entity_id`),
+    KEY `idx_tenant_user_time` (`_tenant_id`, `user_id`, `synced_at`)
+) ENGINE = InnoDB
+  DEFAULT CHARSET = utf8mb4
+  COLLATE = utf8mb4_unicode_ci
+  COMMENT = '数字员工客户端同步记录';