chore: upgrade to pnpm 11.24.0 (#3901)

* chore: upgrade to pnpm 12

* fix: support pnpm 12 in CI

* fix: enable pnpm 12 on Vercel

* refactor: simplify pnpm 12 setup

* refactor: target pnpm 11.24.0

* refactor: let pnpm setup own CI installs

* refactor: limit workspace Node versions

* fix: complete pnpm 11 CI migration