fix(import): remove resourceName/executionRoleArn co-variance refine

The refine required both fields to be set together, but resourceName
is always needed on import (to preserve the AWS name) while
executionRoleArn is only present when the gateway has a custom role.
Gateways without a custom role (service auto-creates one) fail the
refine because resourceName is set but executionRoleArn is not.

Keep the individual field validations (GatewayNameSchema for
resourceName, regex for executionRoleArn).

Author: jesseturner21

src/schema/schemas/mcp.ts

@@ -615,11 +615,7 @@ export const AgentCoreGatewaySchema = z
       message: 'customJwtAuthorizer configuration is required when authorizerType is CUSTOM_JWT',
       path: ['authorizerConfiguration'],
     }
-  )
-  .refine(data => (data.resourceName !== undefined) === (data.executionRoleArn !== undefined), {
-    message: 'resourceName and executionRoleArn must be set together (import) or both omitted (fresh gateway)',
-    path: ['resourceName'],
-  });
+  );
 
 export type AgentCoreGateway = z.infer<typeof AgentCoreGatewaySchema>;