Add targeted Vitest coverage

tests/main.spec.tsx

@@ -0,0 +1,25 @@
+import { describe, expect, test, vi, beforeEach } from 'vitest';
+
+describe('main entry point', () => {
+  beforeEach(() => {
+    vi.resetModules();
+    vi.clearAllMocks();
+    document.body.innerHTML = '<div id="root"></div>';
+  });
+
+  test('renders app when root element exists', async () => {
+    const render = vi.fn();
+    vi.mock('react-dom/client', () => ({ createRoot: () => ({ render }) }));
+
+    await import('../src/main');
+
+    expect(render).toHaveBeenCalled();
+  });
+
+  test('throws when root element is missing', async () => {
+    document.body.innerHTML = '';
+    vi.mock('react-dom/client', () => ({ createRoot: () => ({ render: vi.fn() }) }));
+
+    await expect(import('../src/main')).rejects.toThrow('Root element not found');
+  });
+});