build: update Node.js to v26 and pnpm to v12

[dangreen]

Why

The repository was developed on Node.js 22.18.0 and pnpm 11.9.0, and CI ran on Node.js 22 alone. Node.js 26 is the latest release line and becomes an LTS on 2026-10-28, while the packages keep supporting Node.js 22 until its end of life on 2027-04-30.

pnpm 12 is the latest release, and its breaking changes leave the workspace alone: pnpm 12 recognizes every setting of pnpm-workspace.yaml, nothing passes --frozen-lockfile false, no dependency comes from git, and engineStrict is off.

What

• .tool-versions pins Node.js 26.10.0, the latest 26, and pnpm 12.9.1, the version of the latest tag. Every actions/setup-node step reads Node.js through node-version-file, so a bump of the file moves local development and CI together, and every pnpm/action-setup step asks for pnpm 12.
• The unit job runs on a matrix of Node.js 22, the floor the packages declare, and the version of .tool-versions.

Notes

• Not breaking: engines.node stays >=22 in the packages and the root, so nothing gets released. No package depends on @types/node.
• The lockfile stays as it is: since chore(deps): update dependency vitest to v5 #195 it records linkDirectory: false for the 8 packages whose publishConfig sets it, which pnpm 12, like pnpm 11.28, checks in a frozen install.
• The unit check now reports as unit (22) and unit (.tool-versions). No branch protection or ruleset requires the old name.
• minimumReleaseAge has applied since pnpm 11, so the move to 12 changes nothing about it.
• Checked on Node.js 26.10.0: the workflows parse, a frozen install from scratch on pnpm 11.9.0 and on pnpm 12.9.1 gives no engine warnings and leaves the lockfile alone, the unit tests of oxlint, oxlint-config and scripts pass, oxlint passes on oxlint-config, scripts and lint-package-json, and on pnpm 12 pnpm run lint:package-json passes without an install before the script.
• The Renovate PRs chore(deps): update dependency node to v24 - autoclosed #138, chore(deps): update node.js to v22.23.3 - autoclosed #100, chore(deps): update dependency pnpm to v12 - autoclosed #196 and chore(deps): update dependency pnpm to v11.28.5 - autoclosed #183, which bump Node.js and pnpm, become obsolete.