message: Add notice to `clear-pr-merge-commit-message`
diff: +import React from 'dom-chef';
  import select from 'select-dom';
  import * as pageDetect from 'github-url-detection';
  import features from '../feature-manager';
  import onPrMergePanelOpen from '../github-events/on-pr-merge-panel-open';
  -function init(): void {
  +function init(): void | false {
  const messageField = select('textarea#merge_message_field')!;
  + const originalMessage = messageField.value;
  const deduplicatedAuthors = new Set();
  // This method ensures that "Co-authored-by" capitalization doesn't affect deduplication
  - for (const [, author] of messageField.value.matchAll(/co-authored-by: ([^\n]+)/gi)) {
  + for (const [, author] of originalMessage.matchAll(/co-authored-by: ([^\n]+)/gi)) {
  deduplicatedAuthors.add('Co-authored-by: ' + author);
  }
  - messageField.value = [...deduplicatedAuthors].join('\n');
  + const cleanedMessage = [...deduplicatedAuthors].join('\n');
  + if (cleanedMessage === originalMessage.trim()) {
  + return false;
  + }
  +
  + messageField.value = cleanedMessage;
  + messageField.after(
  + <p className="note rgh-sync-pr-commit-title-note">
  + The description field was cleared by <a target="_blank" href="https://github.com/refined-github/refined-github/wiki/Extended-feature-descriptions#clear-pr-merge-commit-message" rel="noreferrer">Refined GitHub</a>.
  + </p>,
  + <hr/>,
  + );
  }
  void features.add(import.meta.url, {
  