test: add basic test file to api package

- Fixes test failures due to missing test files
- Vitest was exiting with error when no tests found

Author: Umutcan ÖNER

apps/api/src/index.test.ts

@@ -0,0 +1,7 @@
+import { describe, it, expect } from 'vitest';
+
+describe('API', () => {
+  it('should pass basic test', () => {
+    expect(true).toBe(true);
+  });
+});