Light theme default + yt-dlp search fallback

lib/models/subscription_channel.dart

@@ -0,0 +1,13 @@
+class SubscriptionChannel {
+  const SubscriptionChannel({
+    required this.channelId,
+    required this.title,
+    required this.thumbnailUrl,
+    this.description = '',
+  });
+
+  final String channelId;
+  final String title;
+  final String thumbnailUrl;
+  final String description;
+}