feat(integrations): add Vercel MCP connection

[aivong-openhands]

Summary

Adds the official Vercel MCP server as a connection option on the existing Vercel integration in the catalog. Modeled on #482, but Vercel already had a catalog entry, so this extends it instead of adding a new file.

Details

• integrations/catalog/vercel.json:
  • New oauth-mcp connection option: provider: mcp, transport: shttp, URL https://mcp.vercel.com
  • Auth is oauth2 with clientAuthentication: none. The server supports dynamic client registration and PKCE, so no client credentials are needed (same pattern as atlassian-rovo).
  • It is listed before the existing REST oauth option, matching Sentry's oauth-mcp ordering.
  • docsUrl now points to the Vercel MCP docs, and notes explains the sign-in flow.
• integrations/catalog-index.js needs no change. It imports the JSON files, and npm run build:integrations produces no diff.

Validation

• npm run build:integrations leaves catalog-index.js unchanged
• tests/test_integration_catalog_in_sync.py, tests/test_catalog_schema.py and tests/test_catalogs.py pass
• https://mcp.vercel.com/.well-known/oauth-authorization-server advertises a registration endpoint and token_endpoint_auth_methods_supported: ["none"]

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