fix(voice-clone): persist clone info in localStorage, auto-merge into project knobs, fix clone ID detection in CreateModal

- Move voice clone cache from module-level memory to localStorage
  so it survives page refresh and works across browser tabs
- VoiceAvatarPlaceholder now syncs clone result to localStorage
  immediately after creation (both design and clone paths)
- usePodcastProjectState auto-merges voice clone cache into project
  knobs when loading a project (fills gap for projects created
  before voice clone or when voice clone was created after)
- CreateModal now detects voice clone IDs by prefix (vc_*) not
  just by VOICE_CLONE_ID constant, fixing the mismatch where
  VoiceSelector passes the actual clone ID but CreateModal
  expected the placeholder ID
- AudioRegenerateModal is intentionally per-scene override and
  does not write back to knobs (by design)
- trends.py handler added for podcast topic trend analysis

backend/api/podcast/router.py

@@ -12,7 +12,7 @@ from api.story_writer.utils.auth import require_authenticated_user
 from api.story_writer.task_manager import task_manager
 
 # Import all handler routers
-from .handlers import projects, analysis, research, script, audio, images, video, avatar, dubbing, broll
+from .handlers import projects, analysis, research, script, audio, images, video, avatar, dubbing, broll, trends
 
 # Create main router
 router = APIRouter(prefix="/api/podcast", tags=["Podcast Maker"])
@@ -28,6 +28,7 @@ router.include_router(video.router)
 router.include_router(avatar.router)
 router.include_router(dubbing.router)
 router.include_router(broll.router)
+router.include_router(trends.router)
 
 
 @router.get("/task/{task_id}/status")