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/definitions/options-core.ts

@@ -119,6 +119,17 @@ export function buildCoreConfigOptionRegistry(
       description:
         'Comma-separated primary subtitle language priority for managed subtitle auto-selection.',
     },
+    {
+      path: 'youtube.mediaCache.mode',
+      kind: 'enum',
+      enumValues: ['direct', 'background'],
+      enumLabels: {
+        direct: 'Direct stream extraction',
+        background: 'Background media cache',
+      },
+      defaultValue: defaultConfig.youtube.mediaCache.mode,
+      description: 'How YouTube card audio/images are extracted.',
+    },
     {
       path: 'controller.enabled',
       kind: 'boolean',