[codex] Migrate tooling to pnpm

[javorosas]

Summary

• Migrates package management from npm to pnpm 11 with a pnpm lockfile.
• Adds pnpm supply-chain policy settings with minimumReleaseAge: 1440 and blockExoticSubdeps: true.
• Updates CI and deploy workflows to use Node 24 for tooling, installs, builds, and tests while keeping a Node 18 runtime smoke against the built dist artifact.
• Refreshes dev tooling versions and keeps Vite/Playwright on mature versions compatible with the release-age policy.

Validation

• pnpm install --frozen-lockfile
• pnpm run lint
• pnpm test
• pnpm run test:browser
• pnpm audit
• npx -y node@18 --test test/compat/node18-compat.test.cjs