fix: comprehensive error handling and node-level properties validation (fixes #26)

Root cause: AI agents were placing error handling properties inside `parameters` instead of at node level

Major changes:
- Enhanced workflow validator to check for ALL node-level properties (expanded from 6 to 11)
- Added validation for onError property values and deprecation warnings for continueOnFail
- Updated all examples to use modern error handling (onError instead of continueOnFail)
- Added comprehensive node-level properties documentation in tools_documentation
- Enhanced MCP tool documentation for n8n_create_workflow and n8n_update_partial_workflow
- Added test script demonstrating correct node-level property usage

Node-level properties now validated:
- credentials, disabled, notes, notesInFlow, executeOnce
- onError, retryOnFail, maxTries, waitBetweenTries, alwaysOutputData
- continueOnFail (deprecated)

Validation improvements:
- Detects misplaced properties and provides clear fix examples
- Shows complete node structure when properties are incorrectly placed
- Type validation for all node-level boolean and string properties
- Smart error messages with correct placement guidance

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

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

src/services/config-validator.ts

@@ -16,14 +16,14 @@ export interface ValidationResult {
 }
 
 export interface ValidationError {
-  type: 'missing_required' | 'invalid_type' | 'invalid_value' | 'incompatible';
+  type: 'missing_required' | 'invalid_type' | 'invalid_value' | 'incompatible' | 'invalid_configuration';
   property: string;
   message: string;
   fix?: string;
 }
 
 export interface ValidationWarning {
-  type: 'missing_common' | 'deprecated' | 'inefficient' | 'security';
+  type: 'missing_common' | 'deprecated' | 'inefficient' | 'security' | 'best_practice' | 'invalid_value';
   property?: string;
   message: string;
   suggestion?: string;