Refactor SelectedSeatsService to use signals

Replaces internal array state with Angular signals for selected seats. Updates methods to use signal API and adds a new method to filter selected seats by category.

src/app/selected-seats.service.ts

@@ -1,30 +1,31 @@
-import {Injectable} from '@angular/core';
+import { Injectable, signal } from '@angular/core';
 import {Sitzplatz} from '@infinimotion/model-frontend';
 
 @Injectable({
   providedIn: 'root',
 })
 export class SelectedSeatsService {
-  private selectedSeatsList: Sitzplatz[] = [];
+  private selectedSeatsSignal = signal<Sitzplatz[]>([]);
+
+  get selectedSeats() {
+    return this.selectedSeatsSignal;
+  }
 
   pushSelectedSeat(selectedSeat: Sitzplatz): void {
-    this.selectedSeatsList.push(selectedSeat);
-    //console.log("Added" + selectedSeat);
-    //console.log(this.selectedSeatsList);
+    this.selectedSeatsSignal.update(seats => [...seats, selectedSeat]);
   }
 
   removeSelectedSeat(selectedSeat: Sitzplatz): void {
-    let removeId = this.selectedSeatsList.indexOf(selectedSeat);
-
-    if(removeId !== -1) {
-      this.selectedSeatsList.splice(removeId, 1)
-    }
-    //console.log("Removed" + selectedSeat)
-    //console.log(this.selectedSeatsList);
+    this.selectedSeatsSignal.update(seats =>
+      seats.filter(seat => seat.id !== selectedSeat.id)
+    );
   }
 
   getSelectedSeatsList(): Sitzplatz[] {
-    return this.selectedSeatsList;
+    return this.selectedSeatsSignal();
   }
 
+  getSelectedSeatsByCategory(categoryId: number): Sitzplatz[] {
+    return this.selectedSeatsSignal().filter(seat => seat.row.category.id === categoryId);
+  }
 }