fix: implement S3 listBuckets to actually list buckets

- Add @aws-sdk/client-s3 dependency for direct S3 operations
- Fix listBuckets handler which was hardcoded to return empty array
- Now properly queries S3 and returns actual bucket names

ts/plugins.ts

@@ -33,6 +33,10 @@ export {
   smartpromise,
 };
 
+// AWS S3 SDK for direct S3 operations
+import * as s3 from '@aws-sdk/client-s3';
+export { s3 };
+
 // @api.global scope
 import * as typedrequest from '@api.global/typedrequest';
 import * as typedrequestInterfaces from '@api.global/typedrequest-interfaces';