feat: Add comprehensive timeline editor with frame editing and regeneration capabilities

pixelle_video/models/storyboard.py

@@ -73,6 +73,11 @@ class StoryboardFrame:
     duration: float = 0.0                      # Frame duration (seconds, from audio or video)
     created_at: Optional[datetime] = None
     
+    # Quality tracking (added for quality assurance)
+    quality_score: Optional[float] = None      # Overall quality score (0.0-1.0)
+    quality_issues: Optional[List[str]] = None # List of detected quality issues
+    retry_count: int = 0                       # Number of generation retries
+    
     def __post_init__(self):
         if self.created_at is None:
             self.created_at = datetime.now()