drop the built-in Extract Audio entry, and its cache

Extract Audio now exists as a task, with recursion, multi-select scoping, a
format choice and multi-track handling — none of which the one-shot menu entry
had, since it always produced a single mp3.

/extract-audio stays because the file viewer's button plays its output rather
than saving it beside the video, but it no longer returns a cached file: like
transcription and OCR, it always redoes the work. The path is now named outRel,
since it is an output location rather than a cache.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/api/file-browser/router.ts

@@ -849,14 +849,14 @@ router.post('/extract-audio', async (ctx) => {
   const s = await stat(absPath);
   if (s.isDirectory()) throw errors.BAD_REQUEST('Cannot extract audio from a directory');
 
+  // No caching: the extraction is always redone and overwrites the previous result. The output still
+  // lives under the user's data dir because this endpoint backs the file viewer's Extract Audio
+  // button, which plays it rather than saving it beside the video — the Extract Audio task is what
+  // writes into the user's folders.
   const userDataDir = getUserDataDir(user.email);
   const { dir, name } = parsePath(filePath.replace(/^\/+/, ''));
-  const cacheRel = dir ? `cache/audio/${dir}/${name}.mp3` : `cache/audio/${name}.mp3`;
-  const cacheAbs = resolve(userDataDir, cacheRel);
-
-  if (existsSync(cacheAbs)) {
-    return ctx.json({ audioPath: cacheRel, audioRoot: 'user-data', cached: true });
-  }
+  const outRel = dir ? `cache/audio/${dir}/${name}.mp3` : `cache/audio/${name}.mp3`;
+  const cacheAbs = resolve(userDataDir, outRel);
 
   await mkdir(dirname(cacheAbs), { recursive: true });
 
@@ -871,7 +871,7 @@ router.post('/extract-audio', async (ctx) => {
     throw errors.BAD_REQUEST(stderr.trim() || 'Audio extraction failed');
   }
 
-  return ctx.json({ audioPath: cacheRel, audioRoot: 'user-data', cached: false });
+  return ctx.json({ audioPath: outRel, audioRoot: 'user-data', cached: false });
 });
 
 // Extract archive (zip, tar, 7z, rar) into a sibling folder