Add an optional `oauth` config block on MCP server entries in mcp.json, allowing explicit `clientId` and `callbackPort` values for servers that don't expose these through auto-discovery (e.g. Slack). The `oauth.clientId` is used as a fallback — if the server's error response or well-known metadata includes a client_id, that takes precedence. The `callbackPort` defaults to 3000 when not specified.