Light theme default + yt-dlp search fallback

lib/models/playback_option.dart

@@ -0,0 +1,17 @@
+class YoutubePlaybackOption {
+  const YoutubePlaybackOption({
+    required this.height,
+    required this.label,
+    required this.videoUrl,
+    this.audioUrl,
+    this.fps,
+  });
+
+  final int height;
+  final String label;
+  final String videoUrl;
+  final String? audioUrl;
+  final num? fps;
+
+  bool get isAdaptive => audioUrl != null;
+}