Update PR review bot to complete on first approval while still requesting two reviewers

[Copilot]

ℹ️ Issue

📝 Description

The review bot was still waiting on all assigned reviewers before treating a PR as approved, which conflicted with the updated 1-approval merge policy. This change aligns bot completion logic with that policy while preserving two-reviewer assignment for coverage.

Briefly list the changes made to the code:

1. pr-review-status.yml
   • Added approval-threshold logic: PR is treated as complete when any participant has approved and none are currently changes_requested.
   • Updated terminal handling to mark bot state as reviewed when threshold is met (or when all reviewers are done).
   • Updated Slack status/header wording to reflect threshold-based completion.
2. pr-reviewer-remind.yml
   • Switched completion detection to latest per-reviewer state instead of “all assigned reviewed” only.
   • Stops reminders once approval threshold is met; continues reminders only when still pending.
3. .github/AGENTS.md
   • Updated PR review bot workflow docs to match new approval-completion behavior.

const approvalMet = participantStatuses.includes('approved') &&
                    !participantStatuses.includes('changes_requested');

if ((approvalMet || allDone) && prData.status === 'open') {
  prData.status = 'reviewed';
}

✔️ Verification

Provide screenshots of any new components, styling changes, or pages.

Not applicable (workflow/documentation-only change).

🏕️ (Optional) Future Work / Notes

We may want distinct Slack terminal labels for:

• “Approval requirement met” (merge policy satisfied)
• “All requested reviewers responded” (full review coverage complete)