feat: implement integration testing foundation (Phase 1)

Complete implementation of Phase 1 foundation for n8n API integration tests.
Establishes core utilities, fixtures, and infrastructure for testing all 17 n8n API handlers against real n8n instance.

Changes:
- Add integration test environment configuration to .env.example
- Create comprehensive test utilities infrastructure:
  * credentials.ts: Environment-aware credential management (local .env vs CI secrets)
  * n8n-client.ts: Singleton API client wrapper with health checks
  * test-context.ts: Resource tracking and automatic cleanup
  * cleanup-helpers.ts: Multi-level cleanup strategies (orphaned, age-based, tag-based)
  * fixtures.ts: 6 pre-built workflow templates (webhook, HTTP, multi-node, error handling, AI, expressions)
  * factories.ts: Dynamic node/workflow builders with 15+ factory functions
  * webhook-workflows.ts: Webhook workflow configs and setup instructions

- Add npm scripts:
  * test:integration:n8n: Run n8n API integration tests
  * test:cleanup:orphans: Clean up orphaned test resources

- Create cleanup script for CI/manual use

Documentation:
- Add comprehensive integration testing plan (550 lines)
- Add Phase 1 completion summary with lessons learned

Key Features:
- Automatic credential detection (CI vs local)
- Multi-level cleanup (test, suite, CI, orphan)
- 6 workflow fixtures covering common scenarios
- 15+ factory functions for dynamic test data
- Support for 4 HTTP methods (GET, POST, PUT, DELETE) via pre-activated webhook workflows
- TypeScript-first with full type safety
- Comprehensive error handling with helpful messages

Total: ~1,520 lines of production-ready code + 650 lines of documentation

Ready for Phase 2: Workflow creation tests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/integration/n8n-api/scripts/cleanup-orphans.ts

@@ -0,0 +1,43 @@
+#!/usr/bin/env tsx
+/**
+ * Cleanup Orphaned Test Resources
+ *
+ * Standalone script to clean up orphaned workflows and executions
+ * from failed test runs. Run this periodically in CI or manually
+ * to maintain a clean test environment.
+ *
+ * Usage:
+ *   npm run test:cleanup:orphans
+ *   tsx tests/integration/n8n-api/scripts/cleanup-orphans.ts
+ */
+
+import { cleanupAllTestResources } from '../utils/cleanup-helpers';
+import { getN8nCredentials, validateCredentials } from '../utils/credentials';
+
+async function main() {
+  console.log('Starting cleanup of orphaned test resources...\n');
+
+  try {
+    // Validate credentials
+    const creds = getN8nCredentials();
+    validateCredentials(creds);
+
+    console.log(`n8n Instance: ${creds.url}`);
+    console.log(`Cleanup Tag: ${creds.cleanup.tag}`);
+    console.log(`Cleanup Prefix: ${creds.cleanup.namePrefix}\n`);
+
+    // Run cleanup
+    const result = await cleanupAllTestResources();
+
+    console.log('\n✅ Cleanup complete!');
+    console.log(`   Workflows deleted: ${result.workflows}`);
+    console.log(`   Executions deleted: ${result.executions}`);
+
+    process.exit(0);
+  } catch (error) {
+    console.error('\n❌ Cleanup failed:', error);
+    process.exit(1);
+  }
+}
+
+main();