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/translation/__init__.py

@@ -0,0 +1,79 @@
+"""
+Translation Service for ALwrity.
+
+Provides text translation capabilities using multiple providers:
+- DeepL (low-cost, high-quality text translation)
+- WaveSpeed (high-quality video/audio dubbing)
+
+This is a COMMON module that can be used across the entire application:
+- Podcast Maker: Audio/video dubbing
+- Content Creation: Translate blog posts, marketing copy
+- AI Writer: Multilingual content generation
+- Video Studio: Video translation and subtitles
+
+Usage:
+    # Simple usage
+    from services.translation import translate_text, TranslationQuality
+    result = translate_text("Hello world", target_language="Spanish")
+    print(result.translated_text)
+
+    # Advanced usage
+    from services.translation import get_translator
+    translator = get_translator(TranslationQuality.LOW)
+    result = translator.translate(
+        text="Your text here",
+        target_language="fr",
+        source_language="en"
+    )
+
+Environment Variables:
+    DEEPL_API_KEY - DeepL API key for text translation (free tier: 500k chars/month)
+    DEEPL_USE_PRO - Set to "true" for DeepL Pro account
+
+Examples:
+    # Translate a single text
+    >>> from services.translation import translate_text
+    >>> result = translate_text("Hello", target_language="es")
+    >>> print(result.translated_text)
+    Hola
+
+    # Batch translation
+    >>> from services.translation import translate_batch
+    >>> results = translate_batch(
+    ...     texts=["Hello", "Goodbye"],
+    ...     target_language="fr"
+    ... )
+
+    # Check supported languages
+    >>> from services.translation import list_supported_languages
+    >>> langs = list_supported_languages()
+    >>> print(f"Supports {len(langs)} languages")
+"""
+
+from .base_translation import BaseTranslationProvider, TranslationQuality, TranslationResult
+from .deepl_translator import DeepLTranslator
+from .translation_factory import (
+    get_translator,
+    list_supported_languages,
+    translate_text,
+    translate_batch,
+    is_language_supported,
+    clear_translator_cache,
+)
+
+__all__ = [
+    # Enums and dataclasses
+    "TranslationQuality",
+    "TranslationResult",
+    # Classes
+    "BaseTranslationProvider",
+    "DeepLTranslator",
+    # Factory functions
+    "get_translator",
+    "list_supported_languages",
+    "is_language_supported",
+    "clear_translator_cache",
+    # Convenience functions
+    "translate_text",
+    "translate_batch",
+]