Support player names and online join flow

Move SignalR group join into GameManager and add support for player names and improved online join flow.

- Moved Groups.AddToGroupAsync call out of GameHubSocket into GameManager (hubContext.Groups.AddToGroupAsync) so group membership is handled when adding players to a game.
- GUI: added player name input to GameJoinMenu and updated JoinGameObject to include playerName and use string gameCode.
- OnlineMode & LocalMode: constructors updated to instantiate games without passing settings; removed WaitingForOpponent state and cleaned up event bindings.
- OnlineGame: rewrote to handle onGameCreated/onGameJoined/onGameStarted/onFieldUpdated/onGameEnded/onError, added joinGame validation (expects 6-digit code), join flow (connect + join), state updates, drop forwarding to player.drop(gameId, index) and place description updates.
- LocalGame: constructor signature simplified to no-arg.

These changes centralize group management, add player identification, validate join codes, and improve game state/event handling for online play.

GUI/src/routes/OnlineMode.vue

@@ -1,5 +1,7 @@
 <script setup lang="ts">
 import CreateOrJoinMenu from '@/components/CreateOrJoinMenu.vue';
+import Field from '@/components/game/Field.vue';
+import InfoField from '@/components/game/InfoField.vue';
 import GameCreationMenu from '@/components/GameCreationMenu.vue';
 import GameEndedMenu from '@/components/GameEndedMenu.vue';
 import GameJoinMenu from '@/components/GameJoinMenu.vue';
@@ -13,7 +15,6 @@ enum CurrentState {
   CreateOrJoinSelection,
   CreatingGame,
   JoiningGame,
-  WaitingForOpponent,
   Game,
   EndScreen,
 }
@@ -24,11 +25,12 @@ let settings = ref<GameSettings>({
 });
 
 let joiningModel = ref<JoinGameObject>({
+  playerName: 'Spieler 2',
   failed: false,
 });
 
 var currentState = ref<CurrentState>(CurrentState.CreateOrJoinSelection);
-const game = ref<OnlineGame>(new OnlineGame(settings.value));
+const game = ref<OnlineGame>(new OnlineGame());
 const gameField = ref<number[][]>([]);
 const currentSelectionIndex = ref<number | null>(null);
 const gameEndedInformation = ref<GameEnded | null>(null);
@@ -46,11 +48,21 @@ game.value.onGameCreated = (gameCode: string) => {
   settings.value.message = `Das Spiel ist erstellt, deine Freund kann über folgendem Code Beitreten: ${gameCode}`;
 };
 
+game.value.onGameStarted = () => {
+  currentState.value = CurrentState.Game;
+};
+
+game.value.onGameJoinedFailed = () => {
+  joiningModel.value.failed = true;
+};
+
 async function createGame() {
-    await game.value.createGame(settings.value);
+  await game.value.createGame(settings.value);
 }
 
-async function tryToJoin() {}
+async function tryToJoin() {
+  await game.value.joinGame(joiningModel.value);
+}
 </script>
 
 <template>
@@ -62,14 +74,16 @@ async function tryToJoin() {}
 
   <GameCreationMenu
     v-model:settings="settings"
-    @create-game="createGame()"
-    v-else-if="currentState === CurrentState.CreatingGame || currentState === CurrentState.WaitingForOpponent"
+    @create-game="createGame"
+    v-else-if="
+      currentState === CurrentState.CreatingGame
+    "
   />
 
   <GameJoinMenu
     :joinGameObject="joiningModel"
     v-else-if="currentState === CurrentState.JoiningGame"
-    @join="tryToJoin()"
+    @join="tryToJoin"
   />
 
   <GameEndedMenu