Refactor TTS provider management and enhance documentation

- Renamed `bundled-mlx` to `apple-mlx` for clarity in provider types.
- Updated the ProviderSettings component to reflect the new provider naming.
- Improved logging for provider startup and error handling in the backend.
- Added scripts for building and installing PyTorch CPU and CUDA providers locally.
- Enhanced the documentation to include details on TTS provider architecture and development setup.

package.json

@@ -18,6 +18,7 @@
     "build:web": "cd web && bun run build",
     "build:landing": "cd landing && bun run build",
     "build:release": "./scripts/prepare-release.sh",
+    "build:providers": "python scripts/build-providers-local.py",
     "generate:api": "./scripts/generate-api.sh",
     "generate:keys": "cd tauri && bun tauri signer generate -w ~/.tauri/voicebox.key",
     "build:server": "./scripts/build-server.sh",