Keep build errors out of GitHub deployment statuses

[arjunkomath]

Summary

• publish generic failure descriptions for standard and preview GitHub deployments
• retain detailed build errors in control-plane persistence, notifications, and events

Verification

• cd web && pnpm exec vitest run tests/build-status-route.test.ts
• cd web && ./node_modules/.bin/tsc --noEmit

Additional test result

• pnpm test -- build-status-route.test.ts ran the full suite: 519 passed and one unrelated test failed at tests/rollout-certificate-retry.test.ts:182 because it expects the previous handleRolloutFailure signature.

[github-actions]

React Doctor found no new issues. 🎉

_{Reviewed by React Doctor for commit bae4629.}