ci: avoid duplicate build in Node matrix

[rogerchappel]

Summary

• Remove the explicit build from the Node 20/22 compatibility step; pnpm test already runs pnpm run build before template validation, so both matrix versions still build and test without repeating the build.

Verification

• pnpm install --frozen-lockfile — passed
• pnpm test — passed (includes TypeScript build and template registry check)
• bash tests/cli-ux-smoke.sh — passed
• git diff --check — passed
• Confirmed CI matrix remains Node 20 and 22. PR/feature-branch pushes do not match the release workflow's v*.*.* tag trigger; CI's push trigger is restricted to main.

Risk Level

• Low

Rollback Plan

• Revert this one-line CI workflow change.

Human Decision Needed

• None