Parallelize Baseline verification

[ranade-oss]

What changed

• Splits Baseline into independent workflow, backend, frontend, website, and governance jobs.
• Runs those jobs in parallel so actionable failures are visible in one run instead of appearing serially.
• Preserves the final required verify aggregation job, so existing merge gating remains compatible.
• Regenerates only the release manifest during PR verification; other committed generated artifacts remain subject to stale-byte checks.
• Stops release-manifest automation from mutating PR branches and refreshes the committed manifest automatically on main after merges.
• Adds event-driven merging for successful final-head Baseline runs on trusted same-repository agent/ PRs.
• Adds concurrency cancellation for superseded PR heads.

Merge safeguards

The event-driven merger requires an open, non-draft, same-repository agent/ PR from an owner, member, or collaborator. It verifies the exact successful head SHA, rejects requested changes and unresolved review threads, waits briefly for GitHub mergeability calculation, and merges only when GitHub reports the PR as mergeable.

Human-input impact

None. Pull requests trigger Baseline automatically, and eligible agent PRs merge immediately after a successful final-head run. No polling or manual release-manifest refresh is required.

Expected result

Backend, frontend, website, workflow, and governance failures are reported independently and concurrently, while release controls remain enforced without generated-manifest failures masking application errors.