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/services/__init__.py

@@ -9,11 +9,42 @@ from .onboarding.api_key_manager import (
 )
 from .validation import check_all_api_keys
 
+from .translation import (
+    translate_text,
+    translate_batch,
+    get_translator,
+    list_supported_languages,
+    is_language_supported,
+    TranslationQuality,
+    TranslationResult,
+    DeepLTranslator,
+)
+
+from .dubbing import (
+    AudioDubbingService,
+    DubbingResult,
+    VoiceCloneInfo,
+)
+
 __all__ = [
+    # Onboarding
     'APIKeyManager',
     'OnboardingProgress',
     'get_onboarding_progress',
     'StepStatus',
     'StepData',
-    'check_all_api_keys'
-] 
+    'check_all_api_keys',
+    # Translation (common module)
+    'translate_text',
+    'translate_batch',
+    'get_translator',
+    'list_supported_languages',
+    'is_language_supported',
+    'TranslationQuality',
+    'TranslationResult',
+    'DeepLTranslator',
+    # Dubbing
+    'AudioDubbingService',
+    'DubbingResult',
+    'VoiceCloneInfo',
+]