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/api/podcast/handlers/analysis.py

@@ -20,7 +20,7 @@ from services.podcast_bible_service import PodcastBibleService
 from utils.asset_tracker import save_asset_to_library
 from loguru import logger
 import os
-from ..constants import PODCAST_IMAGES_DIR
+from ..constants import get_podcast_media_dir
 from ..models import (
     PodcastAnalyzeRequest, 
     PodcastAnalyzeResponse,
@@ -247,7 +247,8 @@ async def analyze_podcast_idea(
             if image_result and image_result.image_bytes:
                 img_id = str(uuid.uuid4())[:8]
                 filename = f"presenter_podcast_{user_id}_{img_id}.png"
-                avatars_dir = PODCAST_IMAGES_DIR / "avatars"
+                images_dir = get_podcast_media_dir("image", user_id, ensure_exists=True)
+                avatars_dir = images_dir / "avatars"
                 avatars_dir.mkdir(parents=True, exist_ok=True)
                 output_path = avatars_dir / filename