fix: translate custom provider layer

frontend/src/components/providers/ProviderPanel.tsx

@@ -31,6 +31,7 @@ function providerLayerLabel(value: string): string {
     parcels: 'percelen',
     water: 'water',
     landuse: 'landgebruik',
+    custom: 'eigen laag',
   }
   return labels[value] ?? value
 }