Hide game sheet sections and winner selection until game has started

Wrapped WinnerBadge, SheetSection grid, and WinnerCard components in conditional rendering based on `gameStarted` flag derived from game metadata's `started` property. Prevents display of game content in lobby state before host initiates gameplay.

frontend/src/App.jsx

@@ -622,6 +622,7 @@ export default function App() {
     : [];
 
   const isHost = !!(me?.id && gameMeta?.host_user_id && me.id === gameMeta.host_user_id);
+  const gameStarted = !!gameMeta?.started;
 
   return (
     <div style={styles.page}>
@@ -666,16 +667,18 @@ export default function App() {
           onStartGame={startGame}
         />
 
-        {/* Sieger Badge: zwischen Spiel und Verdächtigte Person */}
+        {gameStarted && (
           <WinnerBadge
             winner={{
               display_name: gameMeta?.winner_display_name || "",
               email: gameMeta?.winner_email || "",
             }}
           />
+        )}
 
         <HelpModal open={helpOpen} onClose={() => setHelpOpen(false)} />
 
+        {gameStarted && (
           <div style={{ marginTop: 14, display: "grid", gap: 14 }}>
             {sections.map((sec) => (
               <SheetSection
@@ -689,8 +692,10 @@ export default function App() {
               />
             ))}
           </div>
+        )}
 
         {/* Host-only Winner Auswahl */}
+        {gameStarted && (
           <WinnerCard
             isHost={isHost}
             members={members}
@@ -698,6 +703,7 @@ export default function App() {
             setWinnerUserId={setWinnerUserId}
             onSave={saveWinner}
           />
+        )}
 
         <div style={{ height: 24 }} />
       </div>