Enhance contribution guidelines and improve FloatingGenerateBox component

- Updated CONTRIBUTING.md to include instructions for building with a local Qwen3-TTS development version, facilitating easier testing and development.
- Refactored FloatingGenerateBox component to streamline the rendering of text and instruct fields, improving code readability and maintainability.
- Added functionality to handle auto-resizing of text areas based on content changes, enhancing user experience.
- Improved event handling for keyboard interactions in StoryTrackEditor, allowing for play/pause functionality with the spacebar.
- Introduced a MiniSamplePlayer component in SampleList for better audio playback control, including play, pause, and seek features.
- Implemented sample update functionality in the backend, allowing users to edit reference text for audio samples, with appropriate error handling and user feedback.

app/src/lib/hooks/useModelDownloadToast.tsx

@@ -140,8 +140,8 @@ export function useModelDownloadToast({
       }
     };
 
-    eventSource.onerror = () => {
-      console.error('SSE error');
+    eventSource.onerror = (error) => {
+      console.error('SSE error:', error);
       eventSource.close();
       eventSourceRef.current = null;