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>

src/utils/node-utils.ts

@@ -0,0 +1,46 @@
+/**
+ * Normalizes node type from n8n export format to database format
+ * 
+ * Examples:
+ * - 'n8n-nodes-base.httpRequest' → 'nodes-base.httpRequest'
+ * - '@n8n/n8n-nodes-langchain.agent' → 'nodes-langchain.agent'
+ * - 'nodes-base.slack' → 'nodes-base.slack' (unchanged)
+ * 
+ * @param nodeType The node type to normalize
+ * @returns The normalized node type
+ */
+export function normalizeNodeType(nodeType: string): string {
+  // Handle n8n-nodes-base -> nodes-base
+  if (nodeType.startsWith('n8n-nodes-base.')) {
+    return nodeType.replace('n8n-nodes-base.', 'nodes-base.');
+  }
+  
+  // Handle @n8n/n8n-nodes-langchain -> nodes-langchain
+  if (nodeType.startsWith('@n8n/n8n-nodes-langchain.')) {
+    return nodeType.replace('@n8n/n8n-nodes-langchain.', 'nodes-langchain.');
+  }
+  
+  // Return unchanged if already normalized or unknown format
+  return nodeType;
+}
+
+/**
+ * Gets alternative node type formats to try for lookups
+ * 
+ * @param nodeType The original node type
+ * @returns Array of alternative formats to try
+ */
+export function getNodeTypeAlternatives(nodeType: string): string[] {
+  const alternatives: string[] = [];
+  
+  // Add lowercase version
+  alternatives.push(nodeType.toLowerCase());
+  
+  // If it's just a bare node name, try with common prefixes
+  if (!nodeType.includes('.')) {
+    alternatives.push(`nodes-base.${nodeType}`);
+    alternatives.push(`nodes-langchain.${nodeType}`);
+  }
+  
+  return alternatives;
+}