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/selection-conflict-info/selection-conflict-info.component.html

@@ -0,0 +1,16 @@
+<div class="info-box bg-orange-100 h-22 w-full flex items-center space-x-4 rounded-md p-1 px-3 shadow-sm">
+
+  <div class="w-fit">
+    <mat-icon class="material-symbols-outlined mt-1" style="font-size: 40px; width: 40px; height: 40px;">
+      warning
+    </mat-icon>
+  </div>
+
+  <div class="text-md">
+      <div class="flex space-x-1.5">
+        <h3 class="font-semibold">Sitzplatz aus dem Warenkorb entfernt!</h3>
+      </div>
+      <p>Leider ist der von Ihnen gewählte Sitzplazt nicht mehr verfügbar. Bitte wählen Sie einen anderen.</p>
+  </div>
+
+</div>

src/app/selection-conflict-info/selection-conflict-info.component.ts

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+import { Component } from '@angular/core';
+
+@Component({
+  selector: 'app-selection-conflict-info',
+  standalone: false,
+  templateUrl: './selection-conflict-info.component.html',
+  styleUrl: './selection-conflict-info.component.css',
+})
+export class SelectionConflictInfoComponent {
+
+}