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/workflow-diff-engine.ts

@@ -404,6 +404,7 @@ export class WorkflowDiffEngine {
       notes: operation.node.notes,
       notesInFlow: operation.node.notesInFlow,
       continueOnFail: operation.node.continueOnFail,
+      onError: operation.node.onError,
       retryOnFail: operation.node.retryOnFail,
       maxTries: operation.node.maxTries,
       waitBetweenTries: operation.node.waitBetweenTries,