refactor: address loading review findings (#18)

frontend/src/app/services/session.service.ts

@@ -1,5 +1,5 @@
 import { HttpClient } from '@angular/common/http';
-import { Injectable, inject, signal } from '@angular/core';
+import { computed, Injectable, inject, signal } from '@angular/core';
 
 interface UserResponse {
   authenticated: boolean;
@@ -13,7 +13,7 @@ export type SessionStatus = 'checking' | 'authenticated' | 'anonymous' | 'error'
 export class SessionService {
   private readonly http = inject(HttpClient);
   readonly status = signal<SessionStatus>('checking');
-  readonly isLoggedIn = signal(false);
+  readonly isLoggedIn = computed(() => this.status() === 'authenticated');
   readonly username = signal('');
   readonly email = signal('');
 
@@ -21,13 +21,11 @@ export class SessionService {
     this.status.set('checking');
     this.http.get<UserResponse>('/api/user').subscribe({
       next: (user) => {
-        this.isLoggedIn.set(user.authenticated);
         this.status.set(user.authenticated ? 'authenticated' : 'anonymous');
         this.username.set(user.authenticated ? user.username || 'User' : '');
         this.email.set(user.authenticated ? user.email || '' : '');
       },
       error: () => {
-        this.isLoggedIn.set(false);
         this.status.set('error');
         this.username.set('');
         this.email.set('');