feat: Add Auto-Dubbing feature for Podcast Maker

This commit adds the Auto-Dubbing feature for Podcast Maker with support
for translating podcast audio to different languages with optional voice
cloning to preserve the original speaker's voice.

New Features:
- Translation Service (common module): DeepL integration for low-cost
  translation, WaveSpeed integration for high-quality translation
- Audio Dubbing Service: STT -> Translate -> TTS pipeline with
  voice cloning support
- 9 new API endpoints for dubbing and voice cloning
- Support for 34+ languages
- Cost estimation utilities
- Comprehensive documentation

Files Added:
- services/translation/ (5 files): Translation service module
- services/dubbing/: Audio dubbing service
- api/podcast/handlers/dubbing.py: API endpoints
- docs/AUTO_DUBBING.md: Feature documentation
- CHANGELOG.md: Change log

Files Modified:
- api/podcast/models.py: Added dubbing request/response models
- api/podcast/router.py: Added dubbing routes
- services/__init__.py: Export translation and dubbing services
- scene_animation.py: Fixed missing Path import

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
+from .handlers import projects, analysis, research, script, audio, images, video, avatar, dubbing
 
 # Create main router
 router = APIRouter(prefix="/api/podcast", tags=["Podcast Maker"])
@@ -26,6 +26,7 @@ router.include_router(audio.router)
 router.include_router(images.router)
 router.include_router(video.router)
 router.include_router(avatar.router)
+router.include_router(dubbing.router)
 
 
 @router.get("/task/{task_id}/status")