feat: enhance testing framework with new test cases and configurations

backend/vitest.setup.ts

@@ -0,0 +1,7 @@
+import { vi } from 'vitest'
+
+vi.stubEnv('JWT_SECRET', 'test-secret-for-unit-tests-only')
+vi.stubEnv('NODE_ENV', 'test')
+vi.stubEnv('DB_PATH', ':memory:')
+vi.stubEnv('CORS_ORIGIN', 'http://localhost:5173')
+vi.stubEnv('APP_URL', 'http://localhost:5173')