feat(files): wide file manager layout and basic previews (FM-2)

- Files page uses a wide layout (route handle layout:"wide"): no max width,
  full-height directory tree docked next to the sidebar, resizable
  (200-520px, remembered, double-click resets) and collapsible; mobile keeps
  the tree in a drawer.
- GET /files/preview (admin console session only, same path guards as
  download): text/NFO with encoding detection (BOM/UTF-16/UTF-8/GB18030/Big5),
  subtitles first 200 cues (SRT/VTT/ASS/SSA, PGS timings), .torrent file
  list/trackers (passkey masked)/infohash, image dimensions. Reads at most
  1 MiB of text; .torrent capped at 4 MiB.
- Download also allows text files, .torrent and avif/gif.
- Research notes in docs/design/file-preview-research.md.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/api/files.ts

@@ -2,6 +2,7 @@ import { keepPreviousData, useInfiniteQuery, useMutation, useQuery, useQueryClie
 import {
   cursorPage,
   type FileEntry,
+  FilePreview,
   type FileRef,
   FileRootList,
   FileStat,
@@ -241,57 +242,17 @@ export function fileDownloadUrl(root: string, path: string, inline = false): str
   return `/api/v1/files/download?${qs}`;
 }
 
-/** 文本预览最多读前 256 KB(规格 §9) */
-export const TEXT_PREVIEW_BYTES = 256 * 1024;
-
-export type TextPreview = { text: string; truncated: boolean };
-
-export function useTextPreview(root: string | null, path: string | null, enabled: boolean) {
+/** 结构化预览(FM-2):文本/NFO 带编码探测、字幕前 200 条、.torrent 文件列表、图片尺寸;服务端只读文件头 */
+export function useFilePreview(root: string | null, path: string | null, enabled: boolean) {
   return useQuery({
     queryKey: ["files", "preview", root, path],
     enabled: enabled && !!root && !!path,
     retry: false,
-    queryFn: async ({ signal }): Promise<TextPreview> => {
-      if (filesMockEnabled())
-        return { text: await (await loadMock()).mockPreview(root ?? "", path ?? ""), truncated: false };
-      const res = await fetch(fileDownloadUrl(root ?? "", path ?? ""), { credentials: "include", signal });
-      if (!res.ok) throw new ApiRequestError("internal", `预览失败(HTTP ${res.status})`);
-      return readTextHead(res, TEXT_PREVIEW_BYTES);
-    },
+    staleTime: 30_000,
+    queryFn: ({ signal }) => call(FilePreview, "/files/preview", { params: { root, path }, signal }),
   });
 }
 
-/** 只读响应体前 max 字节(流式,读够就取消),按 UTF-8 解码 */
-async function readTextHead(res: Response, max: number): Promise<TextPreview> {
-  const reader = res.body?.getReader();
-  if (!reader) {
-    const t = await res.text();
-    return { text: t.slice(0, max), truncated: t.length > max };
-  }
-  const chunks: Uint8Array[] = [];
-  let n = 0;
-  let truncated = false;
-  while (n < max) {
-    const { done, value } = await reader.read();
-    if (done || !value) break;
-    chunks.push(value);
-    n += value.length;
-  }
-  if (n >= max) {
-    truncated = n > max || !(await reader.read()).done;
-    await reader.cancel().catch(() => {});
-  }
-  const buf = new Uint8Array(Math.min(n, max));
-  let off = 0;
-  for (const c of chunks) {
-    const part = c.subarray(0, Math.min(c.length, buf.length - off));
-    buf.set(part, off);
-    off += part.length;
-    if (off >= buf.length) break;
-  }
-  return { text: new TextDecoder("utf-8", { fatal: false }).decode(buf), truncated };
-}
-
 /** 整理记录回查:ids 或 planIds(执行后映射到记录);执行中每 3 秒刷新 */
 export function useFileRecords(q: { ids?: string[]; planIds?: string[] }, enabled = true) {
   const ids = q.ids ?? [];