Add .env support for test scripts

- Update test_control_server.py to use python-dotenv
- Read CONTROL_SERVER_URI from environment variable
- Create .env.example with configuration examples
- Test scripts now respect .env configuration for WebSocket URI

.env.example

@@ -0,0 +1,11 @@
+# Lighting Controller Configuration
+
+# WebSocket URI for the control server
+# Used by UI client and test scripts to connect to the control server
+#
+# For local development (running on same machine as control server):
+CONTROL_SERVER_URI=ws://localhost:8765
+#
+# For remote connection (running on different machine from control server):
+# Replace with your control server's IP address
+# CONTROL_SERVER_URI=ws://10.1.1.117:8765