fix: handle empty settings in workflow creation and update comments

Fixed two additional issues discovered in CI testing:

1. cleanWorkflowForCreate() now treats empty settings {} the same as
   missing settings - adds default settings in both cases

2. Updated outdated comments referencing old approach of using empty
   objects for safety

Root Cause:
- Tests were creating workflows with settings: {}
- Empty object {} is truthy in JavaScript, so the check !settings
  passed and no defaults were added
- This caused workflows to be created without proper settings
- Later autofix updates would then fail

Changes:
- Modified cleanWorkflowForCreate() line 107 to check both !settings
  and Object.keys(settings).length === 0
- Updated comment lines 157-172 to reflect current approach
- Now empty settings objects are handled consistently

Testing:
- All 75 unit tests in n8n-validation.test.ts passing
- Fixes CI integration test failures in autofix-workflow.test.ts

Related: #431

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

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

Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en

src/services/n8n-validation.ts

@@ -103,7 +103,8 @@ export function cleanWorkflowForCreate(workflow: Partial<Workflow>): Partial<Wor
   } = workflow;
 
   // Ensure settings are present with defaults
-  if (!cleanedWorkflow.settings) {
+  // Treat empty settings object {} the same as missing settings
+  if (!cleanedWorkflow.settings || Object.keys(cleanedWorkflow.settings).length === 0) {
     cleanedWorkflow.settings = defaultWorkflowSettings;
   }
 
@@ -155,16 +156,17 @@ export function cleanWorkflowForUpdate(workflow: Workflow): Partial<Workflow> {
   //
   // PROBLEM:
   // - Some versions reject updates with settings properties (community forum reports)
-  // - Cloud versions REQUIRE settings property to be present (n8n.estyl.team)
   // - Properties like callerPolicy cause "additional properties" errors
+  // - Empty settings objects {} cause "additional properties" validation errors (Issue #431)
   //
   // SOLUTION:
   // - Filter settings to only include whitelisted properties (OpenAPI spec)
-  // - If no settings provided, use empty object {} for safety
-  // - Empty object satisfies "required property" validation (cloud API)
+  // - If no settings after filtering, omit the property entirely (n8n API rejects empty objects)
+  // - Omitting the property prevents "additional properties" validation errors
   // - Whitelisted properties prevent "additional properties" errors
   //
   // References:
+  // - Issue #431: Empty settings validation error
   // - https://community.n8n.io/t/api-workflow-update-endpoint-doesnt-support-setting-callerpolicy/161916
   // - OpenAPI spec: workflowSettings schema
   // - Tested on n8n.estyl.team (cloud) and localhost (self-hosted)