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/api/handlers.s3.ts

@@ -19,9 +19,15 @@ export async function registerS3Handlers(
           return { buckets: [] };
         }
 
-        // SmartBucket doesn't have a direct listBuckets method
-        // For now return empty - in a full implementation you'd use the underlying S3 client
-        return { buckets: [] };
+        try {
+          const command = new plugins.s3.ListBucketsCommand({});
+          const response = await smartbucket.s3Client.send(command) as plugins.s3.ListBucketsCommandOutput;
+          const buckets = response.Buckets?.map(b => b.Name).filter((name): name is string => !!name) || [];
+          return { buckets };
+        } catch (err) {
+          console.error('Error listing buckets:', err);
+          return { buckets: [] };
+        }
       }
     )
   );