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

app/components/HlsDownloadModal.vue

@@ -0,0 +1,100 @@
+<script setup lang="ts">
+import type { FileItem } from '~/types/file'
+
+const props = defineProps<{
+  open: boolean
+  item: FileItem | null
+}>()
+
+const emit = defineEmits<{
+  'update:open': [value: boolean]
+}>()
+
+const { t } = useI18n()
+const toast = useToast()
+const downloading = ref(false)
+
+watch(() => props.open, (open) => {
+  if (!open) downloading.value = false
+})
+
+async function confirmDownload() {
+  const item = props.item
+  if (!item?.hlsKey || downloading.value) return
+
+  downloading.value = true
+  try {
+    const response = await fetch('/api/files/hls-mp4', {
+      method: 'POST',
+      credentials: 'include',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ key: item.key })
+    })
+
+    if (!response.ok) {
+      const payload = await response.json().catch(() => null) as {
+        error?: { message?: string }
+      } | null
+      throw new Error(payload?.error?.message || t('library.video.downloadMp4Failed'))
+    }
+
+    const blob = await response.blob()
+    const objectUrl = URL.createObjectURL(blob)
+    const dot = item.originalName.lastIndexOf('.')
+    const filename = `${dot > 0 ? item.originalName.slice(0, dot) : item.originalName}.mp4`
+    const link = document.createElement('a')
+    link.href = objectUrl
+    link.download = filename
+    document.body.appendChild(link)
+    link.click()
+    link.remove()
+    setTimeout(() => URL.revokeObjectURL(objectUrl), 0)
+    emit('update:open', false)
+  } catch (error) {
+    toast.add({
+      title: error instanceof Error ? error.message : t('library.video.downloadMp4Failed'),
+      color: 'error'
+    })
+  } finally {
+    downloading.value = false
+  }
+}
+</script>
+
+<template>
+  <UModal
+    :open="open && !!item"
+    :title="t('library.video.downloadMp4Title')"
+    @update:open="emit('update:open', $event)"
+  >
+    <template #body>
+      <p class="text-sm leading-6 text-muted">
+        {{ t('library.video.downloadMp4Confirm') }}
+      </p>
+      <p
+        v-if="downloading"
+        class="mt-3 text-sm text-primary"
+      >
+        {{ t('library.video.downloadMp4Working') }}
+      </p>
+    </template>
+
+    <template #footer>
+      <div class="flex w-full justify-end gap-2">
+        <UButton
+          :label="t('common.cancel')"
+          color="neutral"
+          variant="outline"
+          :disabled="downloading"
+          @click="emit('update:open', false)"
+        />
+        <UButton
+          :label="t('common.continue')"
+          color="primary"
+          :loading="downloading"
+          @click="confirmDownload"
+        />
+      </div>
+    </template>
+  </UModal>
+</template>