Fix WLED target start failing with unexpected zone_mode argument

WLEDProvider.create_client() was not filtering out the zone_mode kwarg
before passing to WLEDClient, causing a 409 error on target start.

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

server/src/wled_controller/core/devices/wled_provider.py

@@ -57,6 +57,7 @@ class WLEDDeviceProvider(LEDDeviceProvider):
         kwargs.pop("baud_rate", None)
         kwargs.pop("send_latency_ms", None)
         kwargs.pop("rgbw", None)
+        kwargs.pop("zone_mode", None)
         return WLEDClient(url, **kwargs)
 
     async def check_health(self, url: str, http_client, prev_health=None) -> DeviceHealth: