fix: require Node.js 24.18.1 and npm 12 and use TypeScript v7

[coderbyheart]

24.18.1 is a security release and NPM v12 also brings important security
improvements.

TypeScript 7 is now GA -> use it instead of the preview version

See https://nodejs.org/en/blog/release/v24.18.1
See https://github.blog/changelog/2026-06-09-upcoming-breaking-changes-for-npm-v12/

• Bump engines to Node.js >=24.18.1 <25 and npm >=12.0.2 <13.
• Add allow-remote=root to .npmrc. npm 12 refuses to fetch
  dependencies from tarball URLs by default; root permits the URLs this
  project declares in its own package.json. This is needed for example for
  dependencies hosted on JSR.
• Install the npm version from engines.npm in CI via a new
  .github/actions/install-npm composite action, so CI uses the version
  the project declares instead of whatever ships with the runner.
• Run TypeScript 6 and 7 side by side: @typescript/native provides
  TypeScript 7 as tsc, while typescript resolves to TypeScript 6 so
  typescript-eslint keeps working. This replaces
  @typescript/native-preview, so npx tsgo becomes npx tsc in the
  pre-commit hook, CI and the docs.

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 1 potential issue.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, have a team admin enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 476e965. Configure here.}