fix: normalize node type prefixes for n8n workflow exports (#71)

- Add centralized normalizeNodeType utility to handle prefix conversion
  - n8n-nodes-base.* → nodes-base.*
  - @n8n/n8n-nodes-langchain.* → nodes-langchain.*
- Update all 9 affected MCP tools to use normalized node types
- AI agents can now use node types directly from n8n workflow exports
- Maintains backward compatibility with existing shortened prefixes
- Add comprehensive test coverage for all affected methods

Fixes #71

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

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.7.17",
+  "version": "2.7.18",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "bin": {