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-main-actions.ts

@@ -53,6 +53,7 @@ export function createBuildTrayMenuTemplateHandler<TMenuItem>(deps: {
     openYomitanSettings: () => void;
     openConfigSettings: () => void;
     openSyncUi: () => void;
+    openYoutubeBrowser: () => void;
     exportLogs: () => void;
     openJellyfinSetup: () => void;
     showJellyfinDiscovery: boolean;
@@ -76,6 +77,7 @@ export function createBuildTrayMenuTemplateHandler<TMenuItem>(deps: {
   openYomitanSettings: () => void;
   openConfigSettingsWindow: () => void;
   openSyncUiWindow: () => void;
+  openYoutubeBrowserWindow: () => void;
   exportLogs: () => void;
   openJellyfinSetupWindow: () => void;
   isJellyfinConfigured: () => boolean;
@@ -124,6 +126,9 @@ export function createBuildTrayMenuTemplateHandler<TMenuItem>(deps: {
       openSyncUi: () => {
         deps.openSyncUiWindow();
       },
+      openYoutubeBrowser: () => {
+        deps.openYoutubeBrowserWindow();
+      },
       exportLogs: () => {
         deps.exportLogs();
       },