feat: implement Phase 5 integration tests (workflow management)

Implemented comprehensive integration tests for workflow deletion and listing:

Test Coverage (16 scenarios):
- delete-workflow.test.ts: 3 tests
  * Successful deletion
  * Error handling for non-existent workflows
  * Cleanup verification

- list-workflows.test.ts: 13 tests
  * No filters (all workflows)
  * Filter by active status (true/false)
  * Filter verification
  * Pagination (first page, cursor, last page)
  * Limit variations (1, 50, 100)
  * Exclude pinned data
  * Empty results
  * Sort order verification

Critical Fixes:
- handleDeleteWorkflow: Now returns deleted workflow data (per n8n API spec)
- handleListWorkflows: Convert tags array to comma-separated string (n8n API format)
- N8nApiClient.deleteWorkflow: Return Workflow object instead of void
- WorkflowListParams.tags: Changed from string[] to string (API expects CSV format)

All 71 integration tests passing.

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

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

tests/integration/n8n-api/workflows/delete-workflow.test.ts

@@ -0,0 +1,132 @@
+/**
+ * Integration Tests: handleDeleteWorkflow
+ *
+ * Tests workflow deletion against a real n8n instance.
+ * Covers successful deletion, error handling, and cleanup verification.
+ */
+
+import { describe, it, expect, beforeEach, afterEach, afterAll } from 'vitest';
+import { createTestContext, TestContext, createTestWorkflowName } from '../utils/test-context';
+import { getTestN8nClient } from '../utils/n8n-client';
+import { N8nApiClient } from '../../../../src/services/n8n-api-client';
+import { SIMPLE_WEBHOOK_WORKFLOW } from '../utils/fixtures';
+import { cleanupOrphanedWorkflows } from '../utils/cleanup-helpers';
+import { createMcpContext } from '../utils/mcp-context';
+import { InstanceContext } from '../../../../src/types/instance-context';
+import { handleDeleteWorkflow } from '../../../../src/mcp/handlers-n8n-manager';
+
+describe('Integration: handleDeleteWorkflow', () => {
+  let context: TestContext;
+  let client: N8nApiClient;
+  let mcpContext: InstanceContext;
+
+  beforeEach(() => {
+    context = createTestContext();
+    client = getTestN8nClient();
+    mcpContext = createMcpContext();
+  });
+
+  afterEach(async () => {
+    await context.cleanup();
+  });
+
+  afterAll(async () => {
+    if (!process.env.CI) {
+      await cleanupOrphanedWorkflows();
+    }
+  });
+
+  // ======================================================================
+  // Successful Deletion
+  // ======================================================================
+
+  describe('Successful Deletion', () => {
+    it('should delete an existing workflow', async () => {
+      // Create workflow
+      const workflow = {
+        ...SIMPLE_WEBHOOK_WORKFLOW,
+        name: createTestWorkflowName('Delete - Success'),
+        tags: ['mcp-integration-test']
+      };
+
+      const created = await client.createWorkflow(workflow);
+      expect(created.id).toBeTruthy();
+      if (!created.id) throw new Error('Workflow ID is missing');
+
+      // Do NOT track workflow since we're testing deletion
+      // context.trackWorkflow(created.id);
+
+      // Delete using MCP handler
+      const response = await handleDeleteWorkflow(
+        { id: created.id },
+        mcpContext
+      );
+
+      // Verify MCP response
+      expect(response.success).toBe(true);
+      expect(response.data).toBeDefined();
+
+      // Verify workflow is actually deleted
+      await expect(async () => {
+        await client.getWorkflow(created.id!);
+      }).rejects.toThrow();
+    });
+  });
+
+  // ======================================================================
+  // Error Handling
+  // ======================================================================
+
+  describe('Error Handling', () => {
+    it('should return error for non-existent workflow ID', async () => {
+      const response = await handleDeleteWorkflow(
+        { id: '99999999' },
+        mcpContext
+      );
+
+      expect(response.success).toBe(false);
+      expect(response.error).toBeDefined();
+    });
+  });
+
+  // ======================================================================
+  // Cleanup Verification
+  // ======================================================================
+
+  describe('Cleanup Verification', () => {
+    it('should verify workflow is actually deleted from n8n', async () => {
+      // Create workflow
+      const workflow = {
+        ...SIMPLE_WEBHOOK_WORKFLOW,
+        name: createTestWorkflowName('Delete - Cleanup Check'),
+        tags: ['mcp-integration-test']
+      };
+
+      const created = await client.createWorkflow(workflow);
+      expect(created.id).toBeTruthy();
+      if (!created.id) throw new Error('Workflow ID is missing');
+
+      // Verify workflow exists
+      const beforeDelete = await client.getWorkflow(created.id);
+      expect(beforeDelete.id).toBe(created.id);
+
+      // Delete workflow
+      const deleteResponse = await handleDeleteWorkflow(
+        { id: created.id },
+        mcpContext
+      );
+
+      expect(deleteResponse.success).toBe(true);
+
+      // Verify workflow no longer exists
+      try {
+        await client.getWorkflow(created.id);
+        // If we reach here, workflow wasn't deleted
+        throw new Error('Workflow should have been deleted but still exists');
+      } catch (error: any) {
+        // Expected: workflow should not be found
+        expect(error.message).toMatch(/not found|404/i);
+      }
+    });
+  });
+});