feat(youtube): add mediaCache mode and safer stream media extraction

- Add `youtube.mediaCache.mode` config option (`direct` | `background`)
- Resolve EDL stream URLs to single audio/video URLs before ffmpeg extraction
- Pass reconnect, user-agent, and safe headers to ffmpeg for remote streams
- Add background yt-dlp media cache with fallback to direct extraction
- Introduce `MediaInput` structured type replacing bare path strings

src/config/settings/registry.ts

@@ -720,6 +720,7 @@ function fieldForLeaf(leaf: Leaf): ConfigSettingsField {
     ...(option?.settingsEnumValues || option?.enumValues
       ? { enumValues: option.settingsEnumValues ?? option.enumValues }
       : {}),
+    ...(option?.enumLabels ? { enumLabels: option.enumLabels } : {}),
     restartBehavior: restartBehaviorForPath(leaf.path),
     advanced:
       leaf.path.startsWith('controller.') ||