Add cancellation and conversion error/success flows

Introduces new components for cancellation and conversion error/success states, updates routing and UI to support resuming and cancelling orders, and refactors seat selection and order handling logic to accommodate these new flows. Also improves seat selection feedback and error handling throughout the checkout process.

src/app/cancellation-success/cancellation-success.component.html

@@ -0,0 +1,11 @@
+<div class="bg-green-200 rounded-md shadow-sm w-full h-fit p-6 py-8 items-center justify-center flex flex-col space-y-2">
+  <mat-icon class="material-symbols-outlined mb-5" style="font-size: 50px; width: 50px; height: 50px">
+    task_alt
+  </mat-icon>
+  <h1 class="text-xl font-bold">Stornierung erfolgreich!</h1>
+  <p class="text-center">Ihre Sitzplätze wurden erfolgreich storniert und stehen wieder zur Buchung zur Verfügnug.</p>
+
+  <button routerLink="/schedule" mat-button matButton="filled" color="accent" class="success-button w-80 mt-4">Zur Programmauswahl</button>
+  <button routerLink="/checkout/performance/{{performanceId()}}" mat-button matButton="outlined" class="success-button w-80 mt-1">Neue Tickets kaufen</button>
+
+</div>