Enhance story item management with trimming, splitting, and duplication features

- Updated StoryTrackEditor and StoryContent components to support trimming and splitting of story items.
- Introduced new API endpoints for trimming, splitting, and duplicating story items, enhancing item management capabilities.
- Refactored related hooks and state management to accommodate new functionalities.
- Improved data models to include trim start and end times for better audio playback control.
- Enhanced UI interactions for selecting and managing story items within the track editor.

app/src/stores/storyStore.ts

@@ -5,6 +5,8 @@ interface StoryPlaybackState {
   // Selection
   selectedStoryId: string | null;
   setSelectedStoryId: (id: string | null) => void;
+  selectedClipId: string | null;
+  setSelectedClipId: (id: string | null) => void;
 
   // Track editor UI state
   trackEditorHeight: number;
@@ -34,6 +36,8 @@ export const useStoryStore = create<StoryPlaybackState>((set, get) => ({
   // Selection
   selectedStoryId: null,
   setSelectedStoryId: (id) => set({ selectedStoryId: id }),
+  selectedClipId: null,
+  setSelectedClipId: (id) => set({ selectedClipId: id }),
 
   // Track editor UI state
   trackEditorHeight: DEFAULT_TRACK_EDITOR_HEIGHT,