Empty Squid worker

Currently we show Kusama NFTs on Polkadot,
Which is not correct, the dummy hack would be that we make `/graphql` endpoint that would alwas return

```json
{
"data": {}
}
```

Start by locating the worker entry point that serves `/graphql` and inspect how Kusama NFT data is currently exposed on Polkadot. Verify the endpoint's current response, then confirm that the empty-worker behavior returns the requested `{ "data": {} }` JSON and no Kusama NFTs; no test or file path is named in the issue.

Written by the indexing model from the issue text.