Fixed type errors caused by changing WorkflowListParams.tags from string[] to string:
1. cleanup-helpers.ts: Changed tags: [tag] to tags: tag (line 221)
2. n8n-api-client.test.ts: Changed tags: ['test'] to tags: 'test,production' (line 384)
3. Added unit tests for handleDeleteWorkflow and handleListWorkflows (100% coverage)
All tests pass, lint clean.
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Co-Authored-By: Claude <noreply@anthropic.com>