feat: voice clone audio generation + podcast workspace architecture

- Voice clone integration: When user selects voice clone in Write phase,
  backend uses their uploaded voice sample + scene script text to generate
  audio via qwen3/minimax/cosyvoice voice clone APIs
- Multi-tenant workspace storage: All podcast assets (audio, video, images,
  charts) now use workspace-specific directories per user
- Chart preview improvements: Card-based B-Roll charts UI with thumbnails,
  takeaway text, and action buttons; public endpoint for image serving
- Voice clone caching: In-memory LRU cache for voice samples (avoids
  re-downloading per scene); frontend caches voice clone metadata
- Thread pool for voice clone: Audio generation uses ThreadPoolExecutor to
  avoid blocking the FastAPI event loop
- Auto-detect voice clone IDs (vc_*, MY_VOICE_CLONE) to route correctly
- DB fallback for voice sample URL: Fetches from ContentAsset if not passed
- Fixed API URL resolution for chart previews
- Fixed GlassyCard DOM warnings for motion props
- Fixed ScriptGenerationProgressView syntax error
- Fixed usePodcastWorkflow scriptData reference

backend/services/podcast_service.py

@@ -86,8 +86,8 @@ class PodcastService:
     ) -> Optional[PodcastProject]:
         """Update project fields."""
         from loguru import logger
-        logger.warning(f"[PodcastService] update_project: user_id={user_id}, project_id={project_id}")
-        logger.warning(f"[PodcastService] update_project: updates={updates}")
+        updated_fields = list(updates.keys()) if isinstance(updates, dict) else []
+        logger.warning(f"[PodcastService] update_project: user_id={user_id}, project_id={project_id}, fields={updated_fields}")
         
         project = self.get_project(user_id, project_id)
         if not project: