feat: implement modal service and components for enhanced user interaction, including modal showcase in demo page

src/app/app.spec.ts

@@ -1,6 +1,12 @@
+import '@angular/compiler';
 import { signal } from '@angular/core';
-import { TestBed } from '@angular/core/testing';
+import { TestBed, getTestBed } from '@angular/core/testing';
+import {
+  BrowserTestingModule,
+  platformBrowserTesting
+} from '@angular/platform-browser/testing';
 import { provideRouter } from '@angular/router';
+import { afterEach, beforeAll, describe, expect, it, vi } from 'vitest';
 
 import { App } from './app';
 import { Tenant } from './core/services/tenant.interface';
@@ -34,6 +40,21 @@ function createTenantServiceStub(status: 'ready' | 'not-found', currentTenant: T
 }
 
 describe('App', () => {
+  beforeAll(() => {
+    try {
+      getTestBed().initTestEnvironment(
+        BrowserTestingModule,
+        platformBrowserTesting()
+      );
+    } catch {
+      // Test environment may already be initialized by another setup entrypoint.
+    }
+  });
+
+  afterEach(() => {
+    TestBed.resetTestingModule();
+  });
+
   it('creates the app when the tenant is ready', async () => {
     await TestBed.configureTestingModule({
       imports: [App],