Replace the outdated backend README (473 lines of stale API docs and
pre-refactor file tree) with a concise architecture document covering
module structure, request flow, backend selection, API domain overview,
and development commands.
Delete REFACTOR_PLAN.md -- all phases are complete.
Update STYLE_GUIDE.md to remove refactor plan references and replace
the verbose target layout with the current actual structure.
- Added support for MLX backend on Apple Silicon, enabling optimized performance for TTS and STT tasks.
- Implemented platform detection to dynamically select between MLX and PyTorch based on the runtime environment.
- Updated build process to include MLX-specific dependencies and configurations for macOS.
- Refactored backend code to improve model loading and inference logic, accommodating backend-specific requirements.
- Enhanced documentation to clarify backend selection and performance benefits for different platforms.
- Streamlined installation instructions and troubleshooting guidance for MLX-related issues.