`baseUrl` has been removed in TypeScript 7. The Docusaurus tsconfig
extends from sets `baseUrl: "."` and `paths: { "@site/*": ["./*"] }`.
Drop the `@docusaurus/tsconfig` extension and inline the needed
options, redefining `paths` so the `@site/*` alias resolves
relative to the tsconfig file (the new TS 7 default for paths).