cloudflare-pages-preview: add comment-mode=repost, extract scripts

New comment-mode input:
- 'sticky' (default, backwards-compat): update the existing marker comment
  in place — same behavior as before
- 'repost': minimize all prior marker comments as OUTDATED (GitHub's native
  hide-comment UI via GraphQL minimizeComment mutation) and post a fresh
  comment at the bottom of the conversation

Useful for /stageblog where each staging should produce a visible new
comment while keeping history collapsible rather than lost.

Both deploy and cleanup accept the input and must match. cleanup in repost
mode minimizes all prior comments and posts a final cleanup note.

Also:
- Extract both comment scripts to sibling comment.js files (same pattern as
  slash-commands/main.js) — the inline YAML scripts were getting long
- Paginate listComments (was only fetching the first 30)

cloudflare-pages-preview/deploy/comment.js

@@ -0,0 +1,76 @@
+// Posts or updates the PR preview-URL comment. Called by actions/github-script
+// via `require(GITHUB_ACTION_PATH + '/comment.js')({ github, context, core })`.
+// All inputs are passed via env vars (see action.yml).
+
+module.exports = async ({ github, context, core }) => {
+  const { owner, repo } = context.repo;
+  const prNumber = Number(process.env.PR_NUMBER);
+  if (!prNumber) {
+    core.info('No PR number available — skipping comment.');
+    return;
+  }
+  const deployUrl = process.env.DEPLOY_URL;
+  const aliasUrl = process.env.ALIAS_URL || deployUrl;
+  const marker = process.env.COMMENT_MARKER;
+  const title = process.env.COMMENT_TITLE;
+  const mode = process.env.COMMENT_MODE;
+  const noindex = process.env.INJECT_NOINDEX === 'true';
+  const commitSha = process.env.COMMIT_SHA;
+
+  const noindexNote = noindex
+    ? ' All pages served with `noindex, nofollow` — search engines will not crawl this preview.'
+    : '';
+
+  const body = [
+    marker,
+    `## ${title}`,
+    '',
+    '| | |',
+    '|---|---|',
+    `| **Preview (stable)** | ${aliasUrl} |`,
+    `| **This commit** | ${deployUrl} |`,
+    `| **Commit** | \`${commitSha.slice(0, 7)}\` |`,
+    '',
+    `_Includes drafts and future-dated posts.${noindexNote}_`,
+  ].join('\n');
+
+  const comments = await github.paginate(github.rest.issues.listComments, {
+    owner, repo, issue_number: prNumber, per_page: 100,
+  });
+  const prior = comments.filter(c =>
+    c.user.type === 'Bot' && c.body && c.body.includes(marker)
+  );
+
+  if (mode === 'repost') {
+    for (const c of prior) {
+      try {
+        await github.graphql(
+          `mutation($id: ID!) {
+             minimizeComment(input: {subjectId: $id, classifier: OUTDATED}) {
+               minimizedComment { isMinimized }
+             }
+           }`,
+          { id: c.node_id },
+        );
+        core.info(`Minimized prior comment ${c.id} as OUTDATED`);
+      } catch (e) {
+        core.warning(`Could not minimize comment ${c.id}: ${e.message}`);
+      }
+    }
+    await github.rest.issues.createComment({
+      owner, repo, issue_number: prNumber, body,
+    });
+  } else {
+    // sticky: update the first prior comment in place, or create one
+    const existing = prior[0];
+    if (existing) {
+      await github.rest.issues.updateComment({
+        owner, repo, comment_id: existing.id, body,
+      });
+    } else {
+      await github.rest.issues.createComment({
+        owner, repo, issue_number: prNumber, body,
+      });
+    }
+  }
+};