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/cli-command-context-main-deps.ts

@@ -67,6 +67,7 @@ export function createBuildCliCommandContextMainDepsHandler(deps: {
   openHachidoriSettings: () => void;
   openConfigSettingsWindow: () => void;
   openSyncUiWindow: () => void;
+  openYoutubeBrowserWindow: () => void;
   cycleSecondarySubMode: () => void;
   openRuntimeOptionsPalette: () => void;
   printHelp: () => void;
@@ -148,6 +149,7 @@ export function createBuildCliCommandContextMainDepsHandler(deps: {
     openHachidoriSettings: () => deps.openHachidoriSettings(),
     openConfigSettingsWindow: () => deps.openConfigSettingsWindow(),
     openSyncUiWindow: () => deps.openSyncUiWindow(),
+    openYoutubeBrowserWindow: () => deps.openYoutubeBrowserWindow(),
     cycleSecondarySubMode: () => deps.cycleSecondarySubMode(),
     openRuntimeOptionsPalette: () => deps.openRuntimeOptionsPalette(),
     printHelp: () => deps.printHelp(),