polygon metaboard subgraph URL in production settings 404s

[thedavidmeister]

Bug

The production registry pinned in `packages/webapp/src/lib/constants.ts` (`rainlanguage/rain.strategies@befb2c3`) names `mb-polygon/0.1` as the polygon metaboard:

```yaml
metaboards:
polygon: https://api.goldsky.com/api/public/project_clv14x04y9kzi01saerx7bxpg/subgraphs/mb-polygon/0.1/gn
```

That subgraph is not deployed in the goldsky `project_clv14x04y9kzi01saerx7bxpg` project. Querying the URL returns:

```
{"statusCode":404,"message":"Subgraph not found. Have you deleted this subgraph recently? If this error persists, please reach out to our support team..."}
```

Polygon metaboard fetches in the production webapp fail.

Fix

Either:

• Deploy a polygon metaboard subgraph and update the settings, or
• Point the polygon metaboard at the right existing deployment (the goldsky project has `metadata-base`, `metadata-arbitrum-one`, and the legacy `mb-base-0x59401C93`, but no polygon metaboard).

Verification

```
curl -X POST 'https://api.goldsky.com/api/public/project_clv14x04y9kzi01saerx7bxpg/subgraphs/mb-polygon/0.1/gn' \
-H 'content-type: application/json' -d '{"query":"{ _meta { block { number } } }"}'
```

Returns HTTP 200 with a 404 body (typical goldsky pattern for missing subgraphs).

Context

Found while auditing goldsky usage for the wider issue at #2556.