Add .env support for transport and sound device configuration

- Add python-dotenv support to control_server.py and sound.py
- Load TRANSPORT from environment variable (default: spi)
- Load AUDIO_INPUT_DEVICE from environment variable (default: 7)
- Load all port configurations from environment variables
- Update .env.example with comprehensive configuration options
- Create .env file with sensible defaults for Pi
- Transport, sound device, and network settings now configurable via .env

Pipfile

@@ -13,6 +13,7 @@ python-rtmidi = "*"
 pyaudio = "*"
 aubio = "*"
 websocket-client = "*"
+python-dotenv = "*"
 
 [dev-packages]