build(deps): update rollup to v4.60.1

[andrejak]

Summary

• update the root rollup devDependency from 3 to 4.60.1
• refresh yarn.lock so the repo no longer installs the older Rollup 3.x line
• add a CI build job that runs corepack yarn build:test on pull requests - this was added to verify that this major upgrade won't break the release... Let me know if you'd rather we skip it

Why

• this repo previously merged a Rollup security upgrade, but the current manifest had drifted back to rollup@3.30.0
• upgrading back to the current 4.x line addresses that regression and aligns the branch with the secure dependency path
• validating the build in CI catches bundler and packaging regressions before merge instead of first surfacing in the release workflow on main

Verification

• corepack yarn test
• corepack yarn build:test
• corepack yarn build && npm pack --dry-run
• npx semantic-release --dry-run --no-ci
• corepack yarn lint (warnings only, no errors)
• corepack yarn npm audit --all (still reports eslint@8.57.1 as a moderate deprecation/support-policy issue, not a Rollup issue)

Linear Issue: TSP-1310