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/types/n8n-api.ts

@@ -9,11 +9,12 @@ export interface WorkflowNode {
   typeVersion: number;
   position: [number, number];
   parameters: Record<string, unknown>;
-  credentials?: Record<string, string>;
+  credentials?: Record<string, unknown>;
   disabled?: boolean;
   notes?: string;
   notesInFlow?: boolean;
   continueOnFail?: boolean;
+  onError?: 'continueRegularOutput' | 'continueErrorOutput' | 'stopWorkflow';
   retryOnFail?: boolean;
   maxTries?: number;
   waitBetweenTries?: number;