For the most part, this is just specifying the pnpm version in a packageManager field in the root package.json.

Then, depending on the environment:

• Github actions: pnpm/action-setup@v4 uses the version automatically - this just removes the version override that disabled that.
• Dockerfile: we need a new corepack enable pnpm && corepack install line, instead of manually installing pnpm.
• Local development: Run corepack enable once (or once per installed node version), then pnpm should automatically use the correct version. No need to manually install pnpm anymore.

This ensures that:

1. We use the same version of pnpm everywhere.
2. We only have one place to update the pnpm version.
3. pnpm version updates will always be explicit - no sudden breaking of installs due to new versions of pnpm being released.

Note that NodeJS may or may not remove corepack from core distributions in the future. Regardless, the packageManager field should stay stable, and there would be other tools continuing support for it.

Other small changes:

• Allow running tests on pull requests from external contributors.
• Bump node version to 22.14.0. Importantly, this contains corepack 0.31.0, which includes the latest npm certificates to allow verifying the latest pnpm version - see this post.