Force transcoding - disable stream copy for downloads

- User can explicitly select 'Copy Original' if they want to copy
- Otherwise always transcode with specified parameters
- Ensures bitrate and resolution settings are respected

src/components/downloadOptionsDialog/downloadOptionsDialog.js

@@ -392,6 +392,12 @@ function buildDownloadUrl(apiClient, item, options) {
         audioStreamIndex: options.audioStreamIndex
     });
 
+    // Force transcoding - disable stream copy
+    // User can select "Copy Original" if they want to copy instead
+    params.set('enableAutoStreamCopy', 'false');
+    params.set('allowVideoStreamCopy', 'false');
+    params.set('allowAudioStreamCopy', 'false');
+
     // Add resolution if not original
     if (options.maxWidth && options.maxWidth !== 'original') {
         params.set('maxWidth', options.maxWidth);