feat: NCS-63 User account implementation (#2)

User Profile info, no game before login/register, menu bar

---------

Co-authored-by: Lala, Shahd <Shahd.Lala@sybit.de>
Co-authored-by: shahdlala66 <shahd.lala66@gmail.com>
Reviewed-on: #2

src/app/models/auth.models.ts

@@ -0,0 +1,28 @@
+export interface LoginRequest {
+  username: string;
+  password: string;
+}
+
+export interface RegisterRequest {
+  username: string;
+  password: string;
+  email?: string;
+}
+
+export interface RegisterResponse {
+  id: string;
+  username: string;
+  rating: number;
+  createdAt: string;
+}
+
+export interface LoginResponse {
+  token: string;
+}
+
+export interface CurrentUser {
+  id: string;
+  username: string;
+  rating: number;
+  createdAt: string;
+}