Add Friday heartbeat Teams notification when no leaderboard changes

On Fridays when the sync finds no changes, post an info card to Teams
showing the last date leaderboard.json was actually changed. Confirms
the automation is running even during quiet weeks.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/skills/sync-nowai-leaderboard/sync.mjs

@@ -108,6 +108,25 @@ async function main() {
   // 4. Change detection.
   if (!hasChanges(oldData, newData)) {
     console.log('[sync] no display changes. Done.');
+    // Friday heartbeat: post a card so the Teams channel confirms the job is alive
+    // even during quiet weeks with no ranking changes.
+    if (new Date().getDay() === 5) {
+      let lastChanged = 'unknown';
+      try {
+        lastChanged = git(root, ['log', '-1', '--format=%as', '--', 'data/leaderboard.json']).trim() || 'unknown';
+      } catch (_) {}
+      await postTeams({
+        kind: 'info',
+        title: '📋 Leaderboard sync — no changes this week',
+        subtitle: subtitle(),
+        facts: [
+          ['Status', 'Up to date — no ranking changes detected'],
+          ['Last changed', lastChanged],
+        ],
+        openUrl: STAGING_URL,
+        openLabel: 'Open staging',
+      });
+    }
     return;
   }
   const changeLines = diffBoards(oldData, newData);