Wire up online game creation and show UI message

Add game creation lifecycle hooks and UI feedback for online games.

- OnlineGame: add onGameCreated and onGameJoinedFailed callbacks, wire player.onGameCreated to set gameId and invoke onGameCreated, and implement createGame to connect and create a game on the player connection. Small cleanup in drop().
- GameSettings: add optional message field to carry informational text to the UI.
- OnlineMode.vue: register handlers for onGameStateChanged, onGameEnded and onGameCreated to update the reactive state and transition to the end/waiting states; update createGame to call OnlineGame.createGame; adjust component rendering logic to include WaitingForOpponent state.
- GameCreationMenu.vue: hide form controls when a settings.message exists and display the message instead; minor layout class adjustments.

These changes enable creating a game, propagating the generated game code to the UI, and showing a message to the user while waiting for opponents.

GUI/src/routes/OnlineMode.vue

@@ -33,7 +33,22 @@ const gameField = ref<number[][]>([]);
 const currentSelectionIndex = ref<number | null>(null);
 const gameEndedInformation = ref<GameEnded | null>(null);
 
-async function createGame() {}
+game.value.onGameStateChanged = (gameState) => {
+  gameField.value = gameState?.currentField ?? [];
+};
+
+game.value.onGameEnded = (gameEndedInfo) => {
+  gameEndedInformation.value = gameEndedInfo;
+  currentState.value = CurrentState.EndScreen;
+};
+
+game.value.onGameCreated = (gameCode: string) => {
+  settings.value.message = `Das Spiel ist erstellt, deine Freund kann über folgendem Code Beitreten: ${gameCode}`;
+};
+
+async function createGame() {
+    await game.value.createGame(settings.value);
+}
 
 async function tryToJoin() {}
 </script>
@@ -48,12 +63,12 @@ async function tryToJoin() {}
   <GameCreationMenu
     v-model:settings="settings"
     @create-game="createGame()"
-    v-if="currentState === CurrentState.CreatingGame"
+    v-else-if="currentState === CurrentState.CreatingGame || currentState === CurrentState.WaitingForOpponent"
   />
 
   <GameJoinMenu
     :joinGameObject="joiningModel"
-    v-if="currentState === CurrentState.JoiningGame"
+    v-else-if="currentState === CurrentState.JoiningGame"
     @join="tryToJoin()"
   />