feat: NCS-69 Challenge request (#3)

- create challange window
- challanges view page
- decline and accept
- notif tab (wip)
- active game window (wip)

---------

Co-authored-by: shahdlala66 <shahd.lala66@gmail.com>
Co-authored-by: Lala, Shahd <Shahd.Lala@sybit.de>
Reviewed-on: #3

src/app/services/challenge-event.service.ts

@@ -0,0 +1,64 @@
+import { Injectable, inject } from '@angular/core';
+import { BehaviorSubject, Observable, Subject } from 'rxjs';
+import { Challenge } from '../models/challenge.models';
+
+/**
+ * Service to manage challenge events via WebSocket
+ * Listens for incoming challenges and emits them to subscribers
+ */
+@Injectable({ providedIn: 'root' })
+export class ChallengeEventService {
+    private readonly incomingChallenges$ = new BehaviorSubject<Challenge[]>([]);
+    private readonly challengeReceived$ = new Subject<Challenge>();
+    private readonly challengeAccepted$ = new Subject<Challenge>();
+    private readonly challengeDeclined$ = new Subject<Challenge>();
+
+    getIncomingChallenges$(): Observable<Challenge[]> {
+        return this.incomingChallenges$.asObservable();
+    }
+
+    getChallengeReceived$(): Observable<Challenge> {
+        return this.challengeReceived$.asObservable();
+    }
+
+    getChallengeAccepted$(): Observable<Challenge> {
+        return this.challengeAccepted$.asObservable();
+    }
+
+    getChallengeDeclined$(): Observable<Challenge> {
+        return this.challengeDeclined$.asObservable();
+    }
+
+    /**
+     * Called when a new challenge is received via WebSocket
+     */
+    onChallengeReceived(challenge: Challenge): void {
+        const current = this.incomingChallenges$.value;
+        this.incomingChallenges$.next([...current, challenge]);
+        this.challengeReceived$.next(challenge);
+    }
+
+    /**
+     * Called when a challenge is accepted
+     */
+    onChallengeAccepted(challenge: Challenge): void {
+        const current = this.incomingChallenges$.value;
+        this.incomingChallenges$.next(current.filter(c => c.id !== challenge.id));
+        this.challengeAccepted$.next(challenge);
+    }
+
+    /**
+     * Called when a challenge is declined or expires
+     */
+    onChallengeRemoved(challengeId: string): void {
+        const current = this.incomingChallenges$.value;
+        this.incomingChallenges$.next(current.filter(c => c.id !== challengeId));
+    }
+
+    /**
+     * Remove a challenge from the incoming list
+     */
+    removeChallenge(challengeId: string): void {
+        this.onChallengeRemoved(challengeId);
+    }
+}