Remove idle color feature, simplify power to turn-off only, fix settings serial port bug

- Remove static/idle color from entire stack (storage, API, processing, UI, CSS, locales)
- Simplify device power button to turn-off only (send black frame, no toggle)
- Send black frame on serial port close (AdalightClient.close)
- Fix settings modal serial port dropdown showing WLED devices due to stale deviceType

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/main.py

@@ -213,7 +213,6 @@ async def lifespan(app: FastAPI):
                 baud_rate=device.baud_rate,
                 software_brightness=device.software_brightness,
                 auto_shutdown=device.auto_shutdown,
-                static_color=device.static_color,
             )
             logger.info(f"Registered device: {device.name} ({device.id})")
         except Exception as e: