pnpm: Project env lockfile can short-circuit package-manager resolution and execute lockfile-selected pnpm bytes

Summary

<!-- maintainer-action:start --> ## Maintainer Action Plan This report is ready to review with the shared patch branch. Start with the PR and the expected fixed behavior, then use the detailed exploit narrative below only if you want to replay the original path. - Advisory: `CAND-PNPM-063` / `GHSA-w466-c33r-3gjp` - Advisory URL: https://github.com/pnpm/pnpm/security/advisories/GHSA-w466-c33r-3gjp - Shared patch PR: https://github.com/pnpm/pnpm-ghsa-j2hc-m6cf-6jm8/pull/1 - Shared patch branch: