fix: address validation improvements from AI agent feedback

- Filter out @version and internal properties from warnings
- Deduplicate validation errors (keep most specific message)
- Add basic code syntax validation for JavaScript and Python
- Check for unbalanced braces/parentheses
- Validate Python indentation consistency
- Add n8n-specific pattern checks (return statements, input access)
- Bump version to 2.4.2

Based on comprehensive AI agent review showing 9.5/10 rating

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.4.1",
+  "version": "2.4.2",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "scripts": {