feat(youtube): add YouTube browser window and Whisper subtitle source

- Add `subminer youtube`/`yt` and tray "Browse YouTube" window that plays or queues picked videos in mpv
- Add `youtube.subtitleSource` (`youtube` | `whisper`) to transcribe YouTube audio via subtitle generation
- Allow the subtitle generation modal on YouTube videos
- Pick the real Japanese track over machine-translated ones and fall back to yt-dlp on HTTP 429
- Remove legacy launcher youtubeSubgen/whisper/AI args and `--youtube-mode`
- Fix EPIPE crash when the launching terminal is closed with Ctrl+C
- Thin media timing review handles with orange original-boundary bars
- Update docs and change fragments

src/core/services/app-lifecycle.test.ts

@@ -18,6 +18,7 @@ function makeArgs(overrides: Partial<CliArgs> = {}): CliArgs {
     hachidori: false,
     settings: false,
     syncWindow: false,
+    youtubeBrowser: false,
     setup: false,
     show: false,
     hide: false,