fix: address code review issues for PR #467

- Add 5-minute TTL to version cache (prevents stale data after upgrades)
- Add type validation for version string from settings response
- Support 'v' prefix in version strings (e.g., v1.2.3)
- Fix race condition in getVersion() using promise-based locking
- Fix empty settings regression (Issue #431) - use minimal defaults

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

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

src/services/n8n-validation.ts

@@ -181,9 +181,17 @@ export function cleanWorkflowForUpdate(workflow: Workflow): Partial<Workflow> {
         filteredSettings[key] = value;
       }
     }
-    cleanedWorkflow.settings = filteredSettings;
+    // If no valid properties remain after filtering, use minimal defaults
+    // Issue #431: n8n API rejects empty settings objects
+    if (Object.keys(filteredSettings).length > 0) {
+      cleanedWorkflow.settings = filteredSettings;
+    } else {
+      // Minimal valid settings - executionOrder v1 is the modern default
+      cleanedWorkflow.settings = { executionOrder: 'v1' as const };
+    }
   } else {
-    cleanedWorkflow.settings = {};
+    // No settings provided - use minimal valid defaults
+    cleanedWorkflow.settings = { executionOrder: 'v1' as const };
   }
 
   return cleanedWorkflow;