feat: 完善媒体管理与备份迁移流程

- 视频上传生成缩略图并提供占位封面和失败原因展示
- 支持 HLS 按需重新封装 MP4，并限制临时文件生命周期与访问权限
- 完善视频、文件 API 文档、搜索、批量删除和单次转码质量参数
- 修复备份恢复与跨后端迁移遗漏缩略图、HLS 清单和分片的问题
- 将备份任务、归档和下载权限按用户隔离
- 增加仅清理当前用户数据的高危存储清空流程和二次文字确认
- 修复 S3 中文文件名元数据及 CLI 数据库连接问题
- 补充备份恢复、用户隔离、媒体资源和转码相关测试

server/utils/storage-backends.ts

@@ -94,6 +94,7 @@ const STORAGE_SCHEMA_TRANSCODE_PROGRESS_KEY = 'storage_schema_transcode_progress
 const STORAGE_SCHEMA_THUMB_KEY = 'storage_schema_thumb'
 const STORAGE_SCHEMA_SOURCE_DELETED_KEY = 'storage_schema_source_deleted'
 const STORAGE_SCHEMA_TRANSCODE_PRESET_KEY = 'storage_schema_transcode_preset'
+const STORAGE_SCHEMA_TRANSCODE_ERROR_KEY = 'storage_schema_transcode_error'
 
 /** images 表新增 media_type 列（区分图床图片与文件床文件） */
 function migrateImagesMediaType(database: DatabaseSync): void {
@@ -232,6 +233,27 @@ function migrateImagesTranscodePreset(database: DatabaseSync): void {
   `).run(STORAGE_SCHEMA_TRANSCODE_PRESET_KEY, new Date().toISOString())
 }
 
+/** images 表新增「转码失败原因」列 */
+function migrateImagesTranscodeError(database: DatabaseSync): void {
+  const migrated = database.prepare(`
+    SELECT value FROM settings WHERE key = ?
+  `).get(STORAGE_SCHEMA_TRANSCODE_ERROR_KEY) as { value?: string } | undefined
+
+  if (migrated?.value === '1') return
+
+  const columns = database.prepare('PRAGMA table_info(images)').all() as Array<{
+    name: string
+  }>
+  if (!columns.some(column => column.name === 'transcode_error')) {
+    database.exec('ALTER TABLE images ADD COLUMN transcode_error TEXT')
+  }
+
+  database.prepare(`
+    INSERT OR REPLACE INTO settings (key, value, updated_at)
+    VALUES (?, '1', ?)
+  `).run(STORAGE_SCHEMA_TRANSCODE_ERROR_KEY, new Date().toISOString())
+}
+
 function migrateStorageTables(database: DatabaseSync): void {
   database.exec(`
     CREATE TABLE IF NOT EXISTS storage_backends (
@@ -263,6 +285,7 @@ function migrateStorageTables(database: DatabaseSync): void {
       thumb_key TEXT,
       source_deleted INTEGER NOT NULL DEFAULT 0,
       transcode_preset TEXT,
+      transcode_error TEXT,
       FOREIGN KEY (backend_id) REFERENCES storage_backends(id)
     );
     CREATE INDEX IF NOT EXISTS idx_images_uploaded_at ON images(uploaded_at DESC);
@@ -284,6 +307,7 @@ function migrateStorageTables(database: DatabaseSync): void {
   migrateImagesThumb(database)
   migrateImagesSourceDeleted(database)
   migrateImagesTranscodePreset(database)
+  migrateImagesTranscodeError(database)
   database.exec(`
     CREATE INDEX IF NOT EXISTS idx_images_media_type ON images(media_type);
   `)