Add .env file support for UI client configuration

- Use python-dotenv to load environment variables
- Add CONTROL_SERVER_URI environment variable for WebSocket connection
- Create .env.example with configuration examples
- Update Pipfile to include python-dotenv dependency
- Allows easy configuration for running UI on desktop pointing to Pi

src/ui_client.py

@@ -15,10 +15,14 @@ import logging
 from async_tkinter_loop import async_handler, async_mainloop
 import websockets
 import websocket
+from dotenv import load_dotenv
+
+# Load environment variables from .env file
+load_dotenv()
 
 # Configuration
 CONFIG_FILE = "config.json"
-CONTROL_SERVER_URI = "ws://localhost:8765"
+CONTROL_SERVER_URI = os.getenv("CONTROL_SERVER_URI", "ws://localhost:8765")
 
 # Dark theme colors
 bg_color = "#2e2e2e"