test: fix workflow validator test using incorrect error output structure

- Update "should validate a perfect workflow" test to use correct n8n error output structure
- Changed from non-existent `error:` property to proper `main[1]` for error outputs
- n8n uses main[0] for success paths and main[1] for error paths, not a separate error property

This fixes the failing test in CI that was introduced with the error output validation enhancements.

🤖 Generated with Claude Code (https://claude.ai/code)

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

tests/unit/services/workflow-validator-comprehensive.test.ts

@@ -1934,8 +1934,10 @@ describe('WorkflowValidator - Comprehensive Tests', () => {
             main: [[{ node: 'HTTP Request', type: 'main', index: 0 }]]
           },
           'HTTP Request': {
-            main: [[{ node: 'Process Data', type: 'main', index: 0 }]],
-            error: [[{ node: 'Error Handler', type: 'main', index: 0 }]]
+            main: [
+              [{ node: 'Process Data', type: 'main', index: 0 }],
+              [{ node: 'Error Handler', type: 'main', index: 0 }]
+            ]
           }
         }
       } as any;