fix(anime): guard playback races and harden install/extract tests

- Tag subtitle cache writes with a generation counter so overlapping playEpisode calls can't clobber the shared cache dir, and don't fail playback when track setup errors
- Ignore stale episode clicks in the detail panel via a LatestRequest guard on playback
- Extract a resetGrid helper in animeui to dedupe grid-clearing logic
- Assert reader cancellation and extracted-file writes actually happen in installer/subsync tests

src/core/services/subsync-extract.test.ts

@@ -185,6 +185,7 @@ test('internal WebVTT extraction uses ffmpeg webvtt muxer with a vtt output file
 
     assert.equal(args[formatIndex + 1], 'webvtt');
     assert.equal(path.extname(result.path), '.vtt');
+    assert.ok(fs.existsSync(result.path), 'the extracted file was not written');
     cleanupTemporaryFile(result);
   } finally {
     fs.rmSync(dir, { recursive: true, force: true });