Enhance story item management with track editing functionality

- Introduced StoryTrackEditor component for managing story item positions and tracks.
- Updated StoriesTab to conditionally render the track editor based on selected story.
- Implemented moveStoryItem API endpoint to handle item repositioning and track changes.
- Enhanced story item data model to include track information.
- Improved audio playback management to support multiple tracks using Web Audio API.
- Added hooks for moving story items and managing playback timing.

app/src/lib/api/client.ts

@@ -20,6 +20,7 @@ import type {
   StoryItemDetail,
   StoryItemBatchUpdate,
   StoryItemReorder,
+  StoryItemMove,
 } from './types';
 
 class ApiClient {
@@ -425,6 +426,13 @@ class ApiClient {
     });
   }
 
+  async moveStoryItem(storyId: string, generationId: string, data: StoryItemMove): Promise<StoryItemDetail> {
+    return this.request<StoryItemDetail>(`/stories/${storyId}/items/${generationId}/move`, {
+      method: 'PUT',
+      body: JSON.stringify(data),
+    });
+  }
+
   async exportStoryAudio(storyId: string): Promise<Blob> {
     const url = `${this.getBaseUrl()}/stories/${storyId}/export-audio`;
     const response = await fetch(url);