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/main/runtime/overlay-runtime-options-main-deps.ts

@@ -41,6 +41,7 @@ export function createBuildInitializeOverlayRuntimeMainDepsHandler(deps: {
   showOverlayNotification?: (payload: OverlayNotificationPayload) => void;
   createFieldGroupingCallback: OverlayRuntimeOptionsMainDeps['createFieldGroupingCallback'];
   getKnownWordCacheStatePath: () => string;
+  getCachedMediaPath?: OverlayRuntimeOptionsMainDeps['getCachedMediaPath'];
   shouldStartAnkiIntegration: () => boolean;
   bindOverlayOwner?: () => void;
   releaseOverlayOwner?: () => void;
@@ -77,6 +78,7 @@ export function createBuildInitializeOverlayRuntimeMainDepsHandler(deps: {
     showOverlayNotification: deps.showOverlayNotification,
     createFieldGroupingCallback: () => deps.createFieldGroupingCallback(),
     getKnownWordCacheStatePath: () => deps.getKnownWordCacheStatePath(),
+    ...(deps.getCachedMediaPath ? { getCachedMediaPath: deps.getCachedMediaPath } : {}),
     shouldStartAnkiIntegration: () => deps.shouldStartAnkiIntegration(),
     bindOverlayOwner: deps.bindOverlayOwner,
     releaseOverlayOwner: deps.releaseOverlayOwner,