feat: download cancellation, duplicate detection, progress tracking improvements

lib/utils/mime_utils.dart

@@ -0,0 +1,24 @@
+String audioMimeTypeForPath(String filePath) {
+  final dotIndex = filePath.lastIndexOf('.');
+  if (dotIndex == -1 || dotIndex == filePath.length - 1) {
+    return 'audio/*';
+  }
+
+  final ext = filePath.substring(dotIndex + 1).toLowerCase();
+  switch (ext) {
+    case 'flac':
+      return 'audio/flac';
+    case 'm4a':
+      return 'audio/mp4';
+    case 'mp3':
+      return 'audio/mpeg';
+    case 'ogg':
+      return 'audio/ogg';
+    case 'wav':
+      return 'audio/wav';
+    case 'aac':
+      return 'audio/aac';
+    default:
+      return 'audio/*';
+  }
+}