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/components/files/model.ts

@@ -519,3 +519,39 @@ export function applyIdentifyCompleted(r: FilesIdentifyResult, p: IdentifyComple
     items: r.items.map((it) => by.get(identifyKey(it)) ?? it),
   };
 }
+
+// ── 预览(FM-2)──
+
+export type PreviewKind = "text" | "subtitle" | "torrent" | "image";
+const PREVIEW_EXT: Record<string, PreviewKind> = {};
+for (const e of "nfo txt log md markdown json xml yaml yml ini conf cfg csv tsv cue sfv md5 sha1 sha256 url".split(" "))
+  PREVIEW_EXT[e] = "text";
+for (const e of "srt vtt ass ssa sup".split(" ")) PREVIEW_EXT[e] = "subtitle";
+for (const e of "jpg jpeg png webp avif gif bmp".split(" ")) PREVIEW_EXT[e] = "image";
+PREVIEW_EXT.torrent = "torrent";
+
+/** 与服务端 preview-parse.ts 同一张扩展名表;目录、链接、无扩展名返回 null */
+export function previewKindOf(e: Pick<FileEntry, "type" | "ext">): PreviewKind | null {
+  if (e.type !== "file" || !e.ext) return null;
+  return PREVIEW_EXT[e.ext.toLowerCase()] ?? null;
+}
+
+/** 毫秒 → 00:01:02.345 */
+export function cueTime(ms: number): string {
+  const h = Math.floor(ms / 3_600_000);
+  const m = Math.floor((ms % 3_600_000) / 60_000);
+  const s = Math.floor((ms % 60_000) / 1000);
+  const f = ms % 1000;
+  const p = (n: number, w = 2) => String(n).padStart(w, "0");
+  return `${p(h)}:${p(m)}:${p(s)}.${p(f, 3)}`;
+}
+
+/** JSON 文本美化;解析失败或已截断时原样返回 */
+export function prettyJson(text: string, truncated: boolean): string {
+  if (truncated) return text;
+  try {
+    return JSON.stringify(JSON.parse(text), null, 2);
+  } catch {
+    return text;
+  }
+}