feat: implement Phase 8 integration tests for system tools

Implement comprehensive integration tests for 3 system tool handlers:
- handleHealthCheck (3 tests): API connectivity, version checking, feature availability
- handleListAvailableTools (7 tests): Tool discovery by category, configuration status, API limitations
- handleDiagnostic (9 tests): Environment checks, API status, tools availability, verbose mode

All 19 tests passing against real n8n instance.

Coverage:
- Health check: API availability verification, version information, feature discovery
- Tool listing: All categories (Workflow Management, Execution Management, System), configuration details
- Diagnostics: Environment variables, API connectivity, tool availability, troubleshooting steps, verbose debug mode

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

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

tests/integration/n8n-api/system/health-check.test.ts

@@ -0,0 +1,109 @@
+/**
+ * Integration Tests: handleHealthCheck
+ *
+ * Tests API health check against a real n8n instance.
+ * Covers connectivity verification and feature availability.
+ */
+
+import { describe, it, expect, beforeEach } from 'vitest';
+import { createMcpContext } from '../utils/mcp-context';
+import { InstanceContext } from '../../../../src/types/instance-context';
+import { handleHealthCheck } from '../../../../src/mcp/handlers-n8n-manager';
+
+describe('Integration: handleHealthCheck', () => {
+  let mcpContext: InstanceContext;
+
+  beforeEach(() => {
+    mcpContext = createMcpContext();
+  });
+
+  // ======================================================================
+  // Successful Health Check
+  // ======================================================================
+
+  describe('API Available', () => {
+    it('should successfully check n8n API health', async () => {
+      const response = await handleHealthCheck(mcpContext);
+
+      expect(response.success).toBe(true);
+      expect(response.data).toBeDefined();
+
+      const data = response.data as any;
+
+      // Verify required fields
+      expect(data).toHaveProperty('status');
+      expect(data).toHaveProperty('apiUrl');
+      expect(data).toHaveProperty('mcpVersion');
+
+      // Status should be a string (e.g., "ok", "healthy")
+      if (data.status) {
+        expect(typeof data.status).toBe('string');
+      }
+
+      // API URL should match configuration
+      expect(data.apiUrl).toBeDefined();
+      expect(typeof data.apiUrl).toBe('string');
+
+      // MCP version should be defined
+      expect(data.mcpVersion).toBeDefined();
+      expect(typeof data.mcpVersion).toBe('string');
+    });
+
+    it('should include feature availability information', async () => {
+      const response = await handleHealthCheck(mcpContext);
+
+      expect(response.success).toBe(true);
+      const data = response.data as any;
+
+      // Check for feature information
+      // Note: Features may vary by n8n instance configuration
+      if (data.features) {
+        expect(typeof data.features).toBe('object');
+      }
+
+      // Check for version information
+      if (data.n8nVersion) {
+        expect(typeof data.n8nVersion).toBe('string');
+      }
+
+      if (data.supportedN8nVersion) {
+        expect(typeof data.supportedN8nVersion).toBe('string');
+      }
+
+      // Should include version note for AI agents
+      if (data.versionNote) {
+        expect(typeof data.versionNote).toBe('string');
+        expect(data.versionNote).toContain('version');
+      }
+    });
+  });
+
+  // ======================================================================
+  // Response Format Verification
+  // ======================================================================
+
+  describe('Response Format', () => {
+    it('should return complete health check response structure', async () => {
+      const response = await handleHealthCheck(mcpContext);
+
+      expect(response.success).toBe(true);
+      expect(response.data).toBeDefined();
+
+      const data = response.data as any;
+
+      // Verify all expected fields are present
+      const expectedFields = ['status', 'apiUrl', 'mcpVersion'];
+      expectedFields.forEach(field => {
+        expect(data).toHaveProperty(field);
+      });
+
+      // Optional fields that may be present
+      const optionalFields = ['instanceId', 'n8nVersion', 'features', 'supportedN8nVersion', 'versionNote'];
+      optionalFields.forEach(field => {
+        if (data[field] !== undefined) {
+          expect(data[field]).not.toBeNull();
+        }
+      });
+    });
+  });
+});