Fix grid import status changing when allow_export is set

The gridImportExport API expects a `disallow_charge_from_grid_with_solar_installed`
parameter (true = disallow), but the `onoff.charge_grid` capability stores the
inverted value (true = allowed). The `allow_export` listener and `flowSetAllowExport`
were passing the capability value without negating it, causing the charge-from-grid
setting to flip whenever the export setting was changed.

https://claude.ai/code/session_011vUXXaaXMLMPQgdM18heMx

Author: claude

drivers/battery/device.ts

@@ -106,7 +106,7 @@ export default class PowerwallDevice extends TeslemetryDevice {
       return this.action(
         this.site.api.gridImportExport(
           value,
-          this.getCapabilityValue("onoff.charge_grid"),
+          !this.getCapabilityValue("onoff.charge_grid"),
         ),
       );
     });
@@ -149,7 +149,7 @@ export default class PowerwallDevice extends TeslemetryDevice {
     await this.action(
       this.site.api.gridImportExport(
         mode,
-        this.getCapabilityValue("onoff.charge_grid"),
+        !this.getCapabilityValue("onoff.charge_grid"),
       ),
     );
   }