test: update tests for v2.28.5 behavior changes (v2.28.6) (#470)

- Update n8n-version tests: 'v' prefix now supported in version strings
- Update n8n-validation tests: empty settings now return minimal defaults
  { executionOrder: 'v1' } instead of {} to avoid API rejection (Issue #431)

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

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

Co-authored-by: Romuald Członkowski <romualdczlonkowski@MacBook-Pro-Romuald.local>
Co-authored-by: Claude <noreply@anthropic.com>

dist/services/n8n-api-client.d.ts

@@ -10,9 +10,10 @@ export declare class N8nApiClient {
     private maxRetries;
     private baseUrl;
     private versionInfo;
-    private versionFetched;
+    private versionPromise;
     constructor(config: N8nApiClientConfig);
     getVersion(): Promise<N8nVersionInfo | null>;
+    private fetchVersionOnce;
     getCachedVersionInfo(): N8nVersionInfo | null;
     healthCheck(): Promise<HealthCheckResponse>;
     createWorkflow(workflow: Partial<Workflow>): Promise<Workflow>;