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

[dangreen]

Why

The repository was developed on Node.js 24.17.0 and pnpm 11.9.0, and CI ran on Node.js 24 with pnpm 11.11.0. Node.js 26 is the latest release line and becomes an LTS on 2026-10-28, while the action itself keeps running on the node24 runtime of action.yml.

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

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.
• engines.node asks for >=24, the runtime of the action, as a hint for contributors. The package is not published to npm, so nothing breaks.

Notes

• minimumReleaseAge has applied since pnpm 11, so the move to 12 changes nothing about it, and minimumReleaseAgeExclude stays as it is.
• 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, a fresh pnpm install --config.node-linker=hoisted, the way the release job runs it, lays the dependencies out flat on pnpm 12, and src/index.js parses. lint-package-json reports only the missing keywords, as it does on main.
• The Renovate PRs chore(deps): update dependency pnpm to v12.11.2 #38, chore(deps): update dependency pnpm to v11.28.5 - autoclosed #24 and chore(deps): update node.js to v24.21.0 - autoclosed #8, which bump Node.js and pnpm, become obsolete.