fix: move useEffect before early returns (React hooks rule violation)

frontend/src/pages/DashboardPage.tsx

@@ -44,6 +44,14 @@ export default function DashboardPage(_props: Props) {
       .catch(() => { setError(true); setLoading(false); });
   }, []);
 
+  // Keep stored streak up to date (hook must be before early returns)
+  const STREAK_KEY = 'tippspiel_last_streak';
+  useEffect(() => {
+    if (data && data.stats.streak > 0) {
+      localStorage.setItem(STREAK_KEY, String(data.stats.streak));
+    }
+  }, [data]);
+
   if (loading) return <div className={styles.loading}>Laden...</div>;
   if (error || !data) return <div className={styles.error}>Dashboard konnte nicht geladen werden.</div>;
 
@@ -53,17 +61,9 @@ export default function DashboardPage(_props: Props) {
   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 */}