docs: align release closeout checklist

[steipete]

Summary

• require the GitHub Release body to match the tagged changelog section before closeout
• document the automated Homebrew formula update and its verification path
• add the required next-patch Unreleased closeout step
• use a Conventional Commit example for the release commit

Proof

• git diff --check
• verified .github/workflows/release.yml dispatches and watches update-formula.yml
• verified the latest GitHub Release contains changelog notes and all six platform archives plus checksums

Risk

Docs only. No runtime, release workflow, version, tag, or published artifact changes.