feat: add week 3 audio and timeline enhancements

backend/app/api/stories.py

@@ -24,6 +24,7 @@ from app.schemas.story_schemas import (
     GenerationRequest,
     GenerationResponse,
     StoryAssetRetryRequest,
+    StoryAudioStatusResponse,
     StorybookRequest,
     StorybookResponse,
     StoryDetailResponse,
@@ -395,8 +396,28 @@ async def get_story_audio(
     db: AsyncSession = Depends(get_db),
 ):
     """Get story audio (MP3)."""
-    audio_bytes = await story_service.generate_story_audio(story_id, user.id, db)
-    return Response(content=audio_bytes, media_type="audio/mpeg")
+    audio_bytes = await story_service.generate_story_audio(story_id, user.id, db)
+    return Response(content=audio_bytes, media_type="audio/mpeg")
+
+
+@router.get("/audio/{story_id}/status", response_model=StoryAudioStatusResponse)
+async def get_story_audio_status(
+    story_id: int,
+    user: User = Depends(require_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Get audio cache status without generating audio."""
+    return await story_service.get_story_audio_status(story_id, user.id, db)
+
+
+@router.delete("/audio/{story_id}/cache", response_model=StoryAudioStatusResponse)
+async def delete_story_audio_cache(
+    story_id: int,
+    user: User = Depends(require_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Clear cached story audio so it can be regenerated."""
+    return await story_service.clear_story_audio_cache(story_id, user.id, db)
 
 
 @router.get("/stories/{story_id}/achievements", response_model=list[AchievementItem])