test: add Phase 4 database integration tests (partial)

- Add comprehensive test utilities for database testing
- Implement connection management tests for in-memory and file databases
- Add transaction tests including nested transactions and savepoints
- Test database lifecycle, error handling, and performance
- Include tests for WAL mode, connection pooling, and constraints

Part of Phase 4: Integration Testing

tests/mocks/n8n-api/index.ts

@@ -0,0 +1,19 @@
+/**
+ * Central export for all n8n API mocks
+ */
+
+export * from './handlers';
+export * from './data/workflows';
+export * from './data/executions';
+export * from './data/credentials';
+
+// Re-export MSW utilities for convenience
+export { http, HttpResponse } from 'msw';
+
+// Export factory utilities
+export { n8nHandlerFactory } from '../setup/msw-setup';
+export { 
+  n8nApiMock, 
+  testDataBuilders,
+  mswTestServer 
+} from '../../integration/setup/msw-test-server';