Add MOS gate control via select entity

Adds a Select entity with four options (Normal / Charge Disabled /
Discharge Disabled / Both Disabled) that sends the 0xE1 write command
to the BMS and immediately refreshes sensor state.  Current option is
derived from the mos_charge_enabled / mos_discharge_enabled bits
already parsed on every poll.

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

custom_components/xiaoxiang_bms/coordinator.py

@@ -7,6 +7,7 @@ from datetime import timedelta
 
 from homeassistant.components.bluetooth import async_ble_device_from_address
 from homeassistant.core import HomeAssistant
+from homeassistant.exceptions import HomeAssistantError
 from homeassistant.helpers.device_registry import DeviceInfo
 from homeassistant.helpers.update_coordinator import DataUpdateCoordinator, UpdateFailed
 
@@ -71,6 +72,19 @@ class BmsCoordinator(DataUpdateCoordinator[dict]):
     async def async_teardown(self) -> None:
         """No-op — each poll disconnects itself."""
 
+    async def async_write_mos(self, value: int) -> None:
+        """Send a MOS control command to the BMS, then refresh sensor state."""
+        device = async_ble_device_from_address(self.hass, self.address, connectable=True)
+        if device is None:
+            raise HomeAssistantError(
+                f"BMS ({self.address}) not reachable — cannot send MOS command"
+            )
+        success = await self._handler.write_mos(device, value)
+        if not success:
+            raise HomeAssistantError("BMS did not acknowledge the MOS command")
+        # Refresh immediately so sensors reflect the new MOS state
+        await self.async_request_refresh()
+
     # ------------------------------------------------------------------
     # Poll
     # ------------------------------------------------------------------