[M1] Complete the bot comment lifecycle

[igbopharaoh]

Tracking

• Milestone: M1 - MVP Correctness Hardening
• Suggested labels: priority:p0, type:hardening, area:api, area:github, milestone:mvp-hardening

Context

Give contributors useful feedback without repeated comments or ambiguous recovery behavior.

Scope

• Update the existing bot comment when a PR remains needs-info.
• Define and document behavior when a PR becomes ready: update, minimize, or leave the old comment.
• Respect the future comments.comment_on_needs_info setting.
• Test draft PRs, repeated edits, and ready PRs.

Acceptance criteria

• A low-readiness PR has at most one active PRGuard guidance comment.
• Draft PRs do not receive needs-info comments.
• The ready-state comment behavior is predictable and documented.

Validation

• Replay repeated PR updates and inspect comment state.

Definition of done

• Relevant Rust, API, or web tests pass.
• Documentation and runbook notes are updated when behavior changes.
• The pull request includes a concise manual verification note.