docs: fix v0.8.0 changelog scope

[Helweg]

Summary

Correct the checked-in v0.8.0 changelog entry so it matches the actual v0.7.0...v0.8.0 release scope, and add a maintainer guardrail so future releases reconcile the full previous-tag delta before publishing notes.

Changes

• expand CHANGELOG.md ## [0.8.0] - 2026-05-14 to cover the shipped worktree fallback/reuse, Zig support, new /peek and /reindex commands, Ollama oversized-input handling, Windows reliability fixes, cleanup/corruption-recovery hardening, and Database.close lifecycle fixes
• tighten README.md release instructions so maintainers compare the previous release tag range against the draft notes before publishing
• update AGENTS.md and .github/release-drafter.yml so the same previous-tag reconciliation step is part of the maintainer checklist and draft-release checklist

Testing

How were these changes tested?

• Unit tests added/updated
• Manual testing performed
• Build passes (npm run build)
• Typecheck passes (npm run typecheck)
• Tests pass (npm run test:run)
• Lint passes (npm run lint)

Release Labels

• Added at least one release category label (feature, bug, performance, documentation, dependencies, refactor, test, chore, or skip-changelog)
• Added at most one semver label (semver:major, semver:minor, semver:patch) when needed

Related Issues

• N/A (follow-up changelog/process correction after publishing v0.8.0)