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/main/runtime/tray-runtime.ts

@@ -46,6 +46,7 @@ export type TrayMenuActionHandlers = {
   openYomitanSettings: () => void;
   openConfigSettings: () => void;
   openSyncUi: () => void;
+  openYoutubeBrowser: () => void;
   exportLogs: () => void;
   openJellyfinSetup: () => void;
   showJellyfinDiscovery: boolean;
@@ -123,6 +124,10 @@ export function buildTrayMenuTemplateRuntime(handlers: TrayMenuActionHandlers):
       label: 'Sync Stats && History',
       click: handlers.openSyncUi,
     },
+    {
+      label: 'Browse YouTube',
+      click: handlers.openYoutubeBrowser,
+    },
     {
       label: 'Export Logs',
       click: handlers.exportLogs,