docs(gator): require inline review comments

[johntmyers]

Summary

Require gator to submit actionable, diff-anchorable findings as inline comments in one batched GitHub review. The review summary and all inline comments now share a single same-SHA disposition.

Related Issue

N/A

Changes

• Require batched pull-request reviews for actionable line-specific findings.
• Define markers and head-SHA semantics for a review with inline comments.
• Add same-SHA guard coverage for batched reviews.

Testing

• bash scripts/agents/gator/bin/gh_guard_test.sh
• Skill validation via quick_validate.py
• git diff --check
• mise run pre-commit (stopped at operator direction; not completed)
• Unit tests added/updated (not applicable)
• E2E tests added/updated (not applicable)

Checklist

• Follows Conventional Commits
• Commit is signed off for DCO compliance