Complete implementation

[RitheeshBaradwaj]

This pull request completes the Mimasa application by finishing the translation pipeline and implementing previously missing features.

• Refactored src/translation/translation.py to orchestrate audio extraction, run audio and video translations concurrently and merge the translated audio back into the processed video using ffmpeg.
• Added a _combine_audio_video helper to handle audio/video muxing and fallback to copying when no audio is produced.
• Updated src/translation/audio_translation.py to separate vocals from music and return the path to the isolated vocals file. The translated audio path is now stored on the instance as translated_audio_file for downstream use.
• Added detailed docstrings and improved logging throughout the translation pipeline.

These changes allow the application to produce a final video with the updated audio track. The translation logic remains stubbed; future work can integrate speech-to-text, machine translation and text-to-speech synthesis.