Refactor and enhance game management, user roles, and state handling

This commit introduces significant changes across the backend and frontend to improve game creation, joining, and member management. Key updates include adding a host role, structured handling of winners, and a New Game modal in the frontend. The refactor also simplifies join codes, improves persistence for user themes, and enhances overall user interaction with better UI feedback and logic.

frontend/src/components/WinnerBadge.jsx

@@ -8,20 +8,29 @@ export default function WinnerBadge({ winnerEmail }) {
     <div
       style={{
         marginTop: 14,
-        padding: "12px 14px",
+        padding: "10px 12px",
         borderRadius: 16,
         border: `1px solid ${stylesTokens.panelBorder}`,
         background: stylesTokens.panelBg,
-        boxShadow: "0 12px 30px rgba(0,0,0,0.45)",
+        boxShadow: "0 12px 30px rgba(0,0,0,0.35)",
         backdropFilter: "blur(6px)",
         display: "flex",
-        gap: 10,
         alignItems: "center",
+        justifyContent: "space-between",
+        gap: 10,
       }}
     >
-      <span style={{ fontSize: 16 }}>🏆</span>
-      <span style={{ fontWeight: 1000, color: stylesTokens.textGold }}>Sieger:</span>
-      <span style={{ color: stylesTokens.textMain }}>{winnerEmail}</span>
+      <div style={{ display: "flex", alignItems: "center", gap: 10 }}>
+        <div style={{ fontSize: 18 }}>🏆</div>
+        <div style={{ color: stylesTokens.textMain, fontWeight: 900 }}>
+          Sieger:
+          <span style={{ color: stylesTokens.textGold }}>{" "}{winnerEmail}</span>
+        </div>
+      </div>
+
+      <div style={{ fontSize: 12, opacity: 0.8, color: stylesTokens.textDim }}>
+        festgelegt
+      </div>
     </div>
   );
 }