feat: 新增视频床与文件床，视频支持 HLS 转码

文件床
- 新增 files/ 存储前缀与 media_type 索引列，图片、视频、文件三类资源独立
- 新增文件上传、列表、删除、批量删除接口，禁止 html/htm/svg
- 支持公开直链与 Token 访问两种模式，后台可切换，直链强制附件下载

视频床
- 新增 videos/ 存储前缀与视频上传接口，单文件上限 500MB
- 接入 ffmpeg 转码队列，并发数与单任务核心数可配，默认串行
- 五档转码质量：直接封装 / 速度 / 平衡 / 质量 / 压缩（压缩档可调码率比例）
- 码率控制避免转码后体积反超源文件，音频跟随源音轨不放大不压缩
- 转码进度实时上报，成功后删除源文件，失败时保留源文件与可用链接
- 上传时自动抽帧生成封面，视频与封面各有独立链接
- 删除视频时中断转码并清理切片、封面与源文件

媒体库
- 图库、视频库、文件库三套独立统计，含趋势、占用与来源分布
- 统一筛选、多选、批量删除、批量标签、网格/列表切换，显示方式按类型分别记忆
- 视频详情对齐图片详情，视频库支持在线播放（hls.js，兼容回退原文件）

修复
- 清理无主的切片、封面与开发期遗留的 ffmpeg 进程
- 源文件按设计删除后，索引不再被启动孤儿清理误删
- 视频统计口径与列表一致，转码中的视频不计入统计
- 转码失败时回收已写入的部分切片，避免残留
- 设置页停用检查更新（与上游版本号已不对应）

其他
- Docker 镜像安装 ffmpeg
- git remote 指向内网仓库

app/composables/useTranscodeSettings.ts

@@ -0,0 +1,114 @@
+interface TranscodeSettingsResponse {
+  concurrency: number
+  threads: number
+  preset: string
+  bitratePercent: number
+  maxConcurrency: number
+  maxThreads: number
+  minBitratePercent: number
+  maxBitratePercent: number
+  presets: string[]
+}
+
+/** 服务端转码参数：并发任务数与单任务 CPU 核心数（仅管理员可改） */
+export function useTranscodeSettings() {
+  const { isAuthenticated, isAdmin, handleAuthError } = useAuth()
+  const toast = useToast()
+  const { t } = useI18n()
+
+  const concurrency = ref(1)
+  const threads = ref(1)
+  const maxConcurrency = ref(8)
+  const maxThreads = ref(64)
+  const preset = ref('veryfast')
+  const presets = ref<string[]>(['veryfast', 'medium', 'slow'])
+  const bitratePercent = ref(80)
+  const minBitratePercent = ref(10)
+  const maxBitratePercent = ref(100)
+  const loaded = ref(false)
+  const hydrated = ref(false)
+
+  let saveTimer: ReturnType<typeof setTimeout> | null = null
+
+  function apply(data: TranscodeSettingsResponse) {
+    hydrated.value = false
+    concurrency.value = data.concurrency
+    threads.value = data.threads
+    preset.value = data.preset
+    bitratePercent.value = data.bitratePercent
+    minBitratePercent.value = data.minBitratePercent ?? 10
+    maxBitratePercent.value = data.maxBitratePercent ?? 100
+    if (data.presets?.length) presets.value = data.presets
+    maxConcurrency.value = data.maxConcurrency
+    maxThreads.value = data.maxThreads
+    loaded.value = true
+    nextTick(() => {
+      hydrated.value = true
+    })
+  }
+
+  async function load() {
+    if (!isAuthenticated.value) return
+    try {
+      apply(await $fetch<TranscodeSettingsResponse>('/api/videos/transcode-settings', {
+        credentials: 'include'
+      }))
+    } catch (error: unknown) {
+      handleAuthError(error)
+      if (isAuthenticated.value) {
+        toast.add({ title: t('preferences.transcodeLoadFailed'), color: 'error' })
+      }
+    }
+  }
+
+  async function save() {
+    if (!hydrated.value || !isAdmin.value) return
+    try {
+      const data = await $fetch<TranscodeSettingsResponse>('/api/videos/transcode-settings', {
+        method: 'PATCH',
+        credentials: 'include',
+        body: {
+          concurrency: concurrency.value,
+          threads: threads.value,
+          preset: preset.value,
+          bitratePercent: bitratePercent.value
+        }
+      })
+      hydrated.value = false
+      concurrency.value = data.concurrency
+      threads.value = data.threads
+      preset.value = data.preset
+      bitratePercent.value = data.bitratePercent
+      nextTick(() => {
+        hydrated.value = true
+      })
+    } catch (error: unknown) {
+      handleAuthError(error)
+      if (isAuthenticated.value) {
+        toast.add({ title: t('preferences.transcodeSaveFailed'), color: 'error' })
+      }
+    }
+  }
+
+  watch([concurrency, threads, preset, bitratePercent], () => {
+    if (!hydrated.value || !isAdmin.value) return
+    if (saveTimer) clearTimeout(saveTimer)
+    saveTimer = setTimeout(() => {
+      void save()
+    }, 600)
+  })
+
+  return {
+    concurrency,
+    threads,
+    preset,
+    bitratePercent,
+    minBitratePercent,
+    maxBitratePercent,
+    presets,
+    maxConcurrency,
+    maxThreads,
+    loaded,
+    load
+  }
+}