Add selection conflict info component and handle seat conflicts

Introduces SelectionConflictInfoComponent to display seat selection conflicts when a seat is removed due to external booking. Removes ShoppingCartComponent and its references. Updates SelectedSeatsService to track conflict state and modifies TheaterOverlayComponent to detect and handle seat conflicts, updating the UI accordingly.

src/app/order/order.component.html

@@ -33,6 +33,10 @@
 
           <div class="performance-info-space"></div>
 
+          @if (selectedSeatsService.hadConflict()) {
+            <app-selection-conflict-info></app-selection-conflict-info>
+          }
+
           <!-- Seat-Selection Overview -->
           <div class="mb-4 p-2">
             @for (seatCategory of seatCategories(); track $index) {

src/app/order/order.component.ts

@@ -1,11 +1,11 @@
 import { SelectedSeatsService } from './../selected-seats.service';
 import { LoadingService } from './../loading.service';
 import { Bestellung, Eintrittskarte, Sitzkategorie, Sitzplatz, Vorstellung } from '@infinimotion/model-frontend';
-import { Component, computed, DestroyRef, EventEmitter, inject, input, output, Output, signal, ViewChild } from '@angular/core';
+import { Component, computed, DestroyRef, inject, input, output, signal } from '@angular/core';
 import { FormBuilder, FormGroup, Validators } from '@angular/forms';
 import { StepperSelectionEvent } from '@angular/cdk/stepper';
 import { HttpService } from '../http.service';
-import { catchError, tap, finalize, switchMap, map, EMPTY, forkJoin } from 'rxjs';
+import { catchError, tap, finalize, EMPTY } from 'rxjs';
 import { MatStepper } from '@angular/material/stepper';
 import { takeUntilDestroyed } from '@angular/core/rxjs-interop';