chore: modernize build tooling and packaging

[tleunen]

Summary

• migrate to vite-plus, publishing dist/index.mjs and dist/index.cjs
• replace ESLint and Prettier config with oxlint and oxfmt, and refresh CI/docs around the new workflow
• remove glob, pkg-up, and reselect, add local package.json discovery for cwd: "packagejson", and expand transformed test helpers to cover vi.*

Testing

• npm run test
• npm run build
• npm run pack --dry-run
• npm run lint

[hiSandog]

The packaging modernization is useful, but the CI matrix has a suspicious mismatch: it runs Node 22.x, 24.x, and 25.x, while the Codecov step checks matrix.node-version == '26.x'. That condition will never be true, so coverage upload is effectively disabled. Since this PR also changes the package to publish ESM/CJS builds, it would be worth adding a pack/install smoke test that imports both entrypoints from the generated tarball.