fix: add DNS mocking to n8n-api-client tests for SSRF protection

Root Cause:
- SSRF protection added DNS resolution via dns/promises.lookup()
- n8n-api-client.test.ts did not mock DNS module
- Tests failed with "DNS resolution failed" error in CI

Fix:
- Added vi.mock('dns/promises') before imports
- Imported dns module for type safety
- Implemented DNS mock in beforeEach to simulate real behavior:
  - localhost → 127.0.0.1
  - IP addresses → returned as-is
  - Real hostnames → 8.8.8.8 (public IP)

Test Results:
- All 50 n8n-api-client tests now pass ✅
- Type checking passes ✅
- Matches pattern from ssrf-protection.test.ts

🤖 Generated with Claude Code

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

tests/unit/services/n8n-api-client.test.ts

@@ -12,6 +12,12 @@ import {
 } from '../../../src/utils/n8n-errors';
 import * as n8nValidation from '../../../src/services/n8n-validation';
 import { logger } from '../../../src/utils/logger';
+import * as dns from 'dns/promises';
+
+// Mock DNS module for SSRF protection
+vi.mock('dns/promises', () => ({
+  lookup: vi.fn(),
+}));
 
 // Mock dependencies
 vi.mock('axios');
@@ -52,7 +58,22 @@ describe('N8nApiClient', () => {
 
   beforeEach(() => {
     vi.clearAllMocks();
-    
+
+    // Mock DNS lookup for SSRF protection
+    vi.mocked(dns.lookup).mockImplementation(async (hostname: any) => {
+      // Simulate real DNS behavior for test URLs
+      if (hostname === 'localhost') {
+        return { address: '127.0.0.1', family: 4 } as any;
+      }
+      // For hostnames that look like IPs, return as-is
+      const ipv4Regex = /^(\d{1,3}\.){3}\d{1,3}$/;
+      if (ipv4Regex.test(hostname)) {
+        return { address: hostname, family: 4 } as any;
+      }
+      // For real hostnames (like n8n.example.com), return a public IP
+      return { address: '8.8.8.8', family: 4 } as any;
+    });
+
     // Create mock axios instance
     mockAxiosInstance = {
       defaults: { baseURL: 'https://n8n.example.com/api/v1' },