feat: 添加图床归档任务支持，优化归档逻辑和错误处理

create_tables.sql

@@ -28,12 +28,20 @@ CREATE TABLE IF NOT EXISTS `image_generations` (
   `upstream_response` JSON NULL COMMENT '完整上游生图接口响应',
   `hosted_response` JSON NULL COMMENT '完整 Lsky 图床上传接口响应',
   `error_message` TEXT NULL COMMENT '失败原因或图床归档失败提示',
+  `archive_status` ENUM('NOT_REQUIRED', 'PENDING', 'RUNNING', 'SUCCEEDED', 'FAILED') NOT NULL DEFAULT 'NOT_REQUIRED' COMMENT '图床归档任务状态',
+  `archive_attempts` INT NOT NULL DEFAULT 0 COMMENT '图床归档已尝试次数',
+  `archive_next_run_at` DATETIME(3) NULL COMMENT '图床归档下次可执行时间',
+  `archive_locked_at` DATETIME(3) NULL COMMENT '图床归档任务被 worker 锁定的时间',
+  `archive_locked_by` VARCHAR(191) NULL COMMENT '图床归档任务 worker 标识',
+  `archive_last_error` TEXT NULL COMMENT '图床归档最近一次失败摘要',
   `created_at` DATETIME(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) COMMENT '创建时间',
   `updated_at` DATETIME(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) ON UPDATE CURRENT_TIMESTAMP(3) COMMENT '更新时间',
   `deleted_at` DATETIME(3) NULL COMMENT '软删除时间',
   PRIMARY KEY (`id`),
   INDEX `image_generations_user_id_created_at_idx` (`user_id`, `created_at`),
   INDEX `image_generations_status_idx` (`status`),
+  INDEX `image_generations_archive_status_archive_next_run_at_idx` (`archive_status`, `archive_next_run_at`),
+  INDEX `image_generations_archive_locked_at_idx` (`archive_locked_at`),
   INDEX `image_generations_deleted_at_idx` (`deleted_at`),
   CONSTRAINT `image_generations_user_id_fkey`
     FOREIGN KEY (`user_id`) REFERENCES `users` (`id`)