feat: rank change arrow (↑/↓) in dashboard stats tile

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

frontend/src/pages/DashboardPage.tsx

@@ -49,6 +49,21 @@ export default function DashboardPage(_props: Props) {
 
   const { hero, stats, nudges } = data;
 
+  const lastRank = parseInt(localStorage.getItem('tippspiel_last_rank') || '0');
+  const rankDiff = lastRank > 0 && stats.rank !== null ? lastRank - stats.rank : 0;
+
+  // Streak break detection via localStorage
+  const STREAK_KEY = 'tippspiel_last_streak';
+  const lastStreak = parseInt(localStorage.getItem(STREAK_KEY) || '0');
+  const streakBroken = lastStreak >= 3 && stats.streak === 0;
+
+  // Keep stored streak up to date when active
+  useEffect(() => {
+    if (stats.streak > 0) {
+      localStorage.setItem(STREAK_KEY, String(stats.streak));
+    }
+  }, [stats.streak]);
+
   return (
     <div className={styles.dashboard}>
       {/* Hero Card */}
@@ -140,7 +155,11 @@ export default function DashboardPage(_props: Props) {
       {/* Stats Row */}
       <div className={styles.statsRow}>
         <div className={`card ${styles.statTile}`}>
-          <span className={styles.statValue}>{stats.rank !== null ? stats.rank : '—'}</span>
+          <span className={styles.statValue}>
+            {stats.rank !== null ? stats.rank : '—'}
+            {rankDiff > 0 && <span className={styles.rankUp}>↑{rankDiff}</span>}
+            {rankDiff < 0 && <span className={styles.rankDown}>↓{Math.abs(rankDiff)}</span>}
+          </span>
           <span className={styles.statLabel}>Dein Rang</span>
         </div>
         <div className={`card ${styles.statTile}`}>