feat: add Angular frontend skeleton

frontend/src/app/services/api-config.token.ts

@@ -0,0 +1,7 @@
+import { InjectionToken } from '@angular/core';
+
+import { environment } from '../environments/environment';
+
+export const API_BASE_URL = new InjectionToken<string>('API_BASE_URL', {
+  factory: () => environment.apiBaseUrl,
+});