feat(editor): 剪辑成片验收闭环 - 概览渲染计数、导入/字幕/预览修复与本地 whisper 转写运行时 (#414)

* feat(editor): 剪辑成片验收闭环 - 概览渲染成功计数、媒体导入/字幕/预览修复与本地 whisper 转写运行时

- 概览:渲染成功计数接入项目概览 SQL/JSON,成片状态随 timeline_render 任务联动
- 修复:本地媒体导入后列表为空(挂载时服务端重同步 + 导入后校验重取)、
  字幕工具残留 M6 占位文案、预览监视器悬浮遮挡层改为顶部信息条、
  生成任务轮询连续查询失败即抛错不再空转至超时
- 本地转写:新增 scripts/start-whisper-local.sh 一键启动 whisper.cpp,
  local-development 文档补安装/启动/后端注入指引
- 同步 docs(overview/features、pending-test、index)

* fix(assets): 素材库封面未知 kind 兜底,避免 AssetCover 渲染崩溃

运行时素材记录若带未知/脏 kind(历史遗留或本地存储异常),assetKindIcons[asset.kind]
得到 undefined,AssetCover/AssetDrawer 渲染 <KindIcon/> 触发
'Element type is invalid ... got: undefined' 使 /assets 整页崩溃。
新增 isKnownAssetKind 守卫:未知 kind 回退 FileText 图标与通用文案,脏数据不再崩页。

* fix(editor): mp4v 播放死循环修复——MPEG-4 Part 2 归入播放转码通道，监视器加终态护栏

- 后端把 mp4v 与 H.264/AV1/VP9 一并判为浏览器可播 → playbackStatus=none；
  Chromium/Firefox/Edge 实际均不支持 MPEG-4 Part 2，原件解码即失败。
  现将其并入 H.265 转码通道(转 H.264 兼容副本)；损坏文件转码失败落
  failed，前端据此显示终止性错误而非死循环。
- 前端监视器轮询到 none/failed 或超时后不再回退 primary 重试；副本 URL
  回退原件反复触发 onError 时保持终态文案，不再覆盖成"正在生成兼容版本"。

* feat(editor): 画布产物自动同步剪辑素材库，素材面板新增「画布素材」分组

- 打开剪辑器时自动把画布工作台当前采用(storyboard/action_board/分镜/导出成片，
  ready 且有资源)的产物 linkProjectAsset(source=canvas) 并入项目素材库；
  后端幂等、前端按 storageKey+会话 ref 去重，失败静默下次进入自动补同步。
- LinkProjectAsset 支持 source 白名单(uploaded/canvas)并写入素材 payload，
  供素材面板按来源分组；面板新增「画布素材」页签与分组，与「本地上传」「项目素材」并列。
- 补 source=canvas 写入断言测试。

* docs(progress): 记录 mp4v 播放死循环修复与画布产物素材同步的待浏览器验收项

web/src/pages/assets/index.tsx

@@ -1097,8 +1097,13 @@ function AssetCard({
     );
 }
 
+function isKnownAssetKind(kind: unknown): kind is AssetKind {
+    return kind === "image" || kind === "video" || kind === "audio" || kind === "model" || kind === "text";
+}
+
 function AssetCover({ asset, selected, isTrash = false, onSelect, onOpen, menuItems }: { asset: LibraryAsset; selected: boolean; isTrash?: boolean; onSelect: (selected: boolean) => void; onOpen: () => void; menuItems: MenuProps["items"] }) {
-    const KindIcon = assetKindIcons[asset.kind];
+    const kind = isKnownAssetKind(asset.kind) ? asset.kind : undefined;
+    const KindIcon = kind ? assetKindIcons[kind] : FileText;
     const clock = asset.kind === "video" || asset.kind === "audio" ? formatAssetClock(asset.data.durationMs) : null;
     const showPlay = asset.kind === "video";
     const isLight = asset.kind === "audio" || asset.kind === "text" || asset.kind === "model";
@@ -1133,7 +1138,7 @@ function AssetCover({ asset, selected, isTrash = false, onSelect, onOpen, menuIt
             <span className="assets-cover-badges">
                 <span className="assets-cover-badge is-kind">
                     <KindIcon />
-                    {assetKindLabel(asset.kind)}
+                    {kind ? assetKindLabel(kind) : "素材"}
                 </span>
                 {isTrash ? <span className="assets-cover-badge is-category !bg-amber-500/85 !text-white">回收站</span> : <span className="assets-cover-badge is-category">{assetCategoryLabel(asset.category)}</span>}
             </span>
@@ -1320,7 +1325,8 @@ function AssetFilterGroup({
 
 function AssetDrawer({ asset, onClose, onCopy, onDownload }: { asset: LibraryAsset | null; onClose: () => void; onCopy: (asset: LibraryAsset) => void; onDownload: (asset: LibraryAsset) => void }) {
     const facts = asset ? assetArchiveFacts(asset) : [];
-    const KindIcon = asset ? assetKindIcons[asset.kind] : Clapperboard;
+    const kind = asset && isKnownAssetKind(asset.kind) ? asset.kind : undefined;
+    const KindIcon = asset ? (kind ? assetKindIcons[kind] : FileText) : Clapperboard;
     return (
         <Drawer className="library-drawer" title="素材档案" open={Boolean(asset)} size="large" onClose={onClose}>
             {asset ? (