feat(game-info): add placeholder and disable bet input

frontend/src/app/feature/game/blackjack/components/game-info/game-info.component.ts

@@ -67,10 +67,12 @@ import { BettingService } from '@blackjack/services/betting.service';
               type="number"
               id="bet"
               formControlName="bet"
-              class="w-full px-3 py-2 bg-deep-blue-light text-white rounded focus:outline-none focus:ring-2 focus:ring-emerald"
+              class="w-full px-3 py-2 bg-deep-blue-light text-white rounded focus:outline-none focus:ring-2 focus:ring-emerald disabled:opacity-50"
               [min]="1"
               [max]="balance"
               step="0.01"
+              [disabled]="gameInProgress || isActionInProgress"
+              [placeholder]="balance | currency: 'EUR'"
             />
             @if (betForm.get('bet')?.errors?.['required'] && betForm.get('bet')?.touched) {
               <span class="text-xs text-accent-red">Bitte geben Sie einen Einsatz ein</span>