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]>

packages/contracts/src/api.ts

@@ -1540,10 +1540,20 @@ export const Api = {
       path: "/files/download",
       scope: "admin",
       auth: "session",
-      summary: "下载小文件（nfo/字幕/图片，≤20 MiB；流式；仅管理员控制台会话；审计）",
+      summary: "下载小文件（nfo/字幕/图片/文本/.torrent，≤20 MiB；流式；仅管理员控制台会话；审计）",
       query: files.FilesDownloadQuery,
       response: files.FilesDownloadResponse,
     }),
+    preview: ep({
+      method: "get",
+      path: "/files/preview",
+      scope: "admin",
+      auth: "session",
+      summary:
+        "结构化预览（文本/NFO 前 1 MiB 带编码探测、字幕前 200 条、.torrent 文件列表、图片尺寸；仅管理员控制台会话）",
+      query: files.FilesPreviewQuery,
+      response: files.FilePreview,
+    }),
     records: ep({
       method: "get",
       path: "/files/records",

packages/contracts/src/files.ts

@@ -728,6 +728,70 @@ export type FilesDownloadQuery = z.infer<typeof FilesDownloadQuery>;
 /** OpenAPI 描述用:实际响应为二进制流 */
 export const FilesDownloadResponse = z.string().describe("文件内容（application/octet-stream 等）");
 
+// 预览(FM-2):GET /files/preview 返回结构化预览,仅管理员会话,路径守卫同下载。
+// 文本/字幕最多读前 1 MiB 并探测编码(BOM / UTF-8 / UTF-16 / GB18030 / Big5);字幕解析前 200 条;
+// .torrent ≤ 4 MiB 解析文件列表、tracker 与 infohash;图片只回尺寸类型信息,内容走 /files/download?inline=true。
+export const FilesPreviewQuery = z.object({ root: FileRootId, path: FileRelPath });
+export type FilesPreviewQuery = z.infer<typeof FilesPreviewQuery>;
+
+export const SubtitleCue = z.object({
+  /** 毫秒 */
+  start: NonNegInt,
+  end: NonNegInt,
+  /** 去掉样式标签后的纯文本;图形字幕(sup)为空串 */
+  text: z.string(),
+});
+export type SubtitleCue = z.infer<typeof SubtitleCue>;
+
+const PreviewBase = z.object({ size: NonNegInt });
+export const FilePreview = z.discriminatedUnion("type", [
+  PreviewBase.extend({
+    type: z.literal("text"),
+    /** 小写扩展名(nfo/txt/log/md/json/xml/yaml…) */
+    format: z.string(),
+    /** 探测出的编码名(utf-8 / utf-16le / utf-16be / gb18030 / big5 / windows-1252) */
+    encoding: z.string(),
+    text: z.string(),
+    truncated: z.boolean(),
+  }),
+  PreviewBase.extend({
+    type: z.literal("subtitle"),
+    format: z.enum(["srt", "vtt", "ass", "ssa", "sup"]),
+    encoding: z.string().nullable(),
+    cues: z.array(SubtitleCue),
+    /** 读到的范围内共解析出多少条(可能大于 cues.length) */
+    parsed: NonNegInt,
+    /** 只读了文件前一部分 */
+    truncated: z.boolean(),
+    /** ASS/SSA 的 [Script Info] Title */
+    title: z.string().nullable(),
+  }),
+  PreviewBase.extend({
+    type: z.literal("torrent"),
+    name: z.string(),
+    hash: z.string(),
+    infohashV1: z.string().nullable(),
+    infohashV2: z.string().nullable(),
+    private: z.boolean(),
+    totalSize: NonNegInt,
+    fileCount: NonNegInt,
+    /** 最多 500 个 */
+    files: z.array(z.object({ path: z.string(), length: NonNegInt })),
+    trackers: z.array(z.string()),
+    comment: z.string().nullable(),
+    createdBy: z.string().nullable(),
+    createdAt: Timestamp.nullable(),
+    pieceLength: NonNegInt.nullable(),
+  }),
+  PreviewBase.extend({
+    type: z.literal("image"),
+    mime: z.string(),
+    width: NonNegInt.nullable(),
+    height: NonNegInt.nullable(),
+  }),
+]);
+export type FilePreview = z.infer<typeof FilePreview>;
+
 // 整理记录回查(W5-A2,只读):整理页 `/console/organize?ids=` 预填;planIds 为 /files/move|copy|organize 的 planId
 
 const csvIds = z