Implement n8n-MCP integration

This commit adds a complete integration between n8n workflow automation and the Model Context Protocol (MCP):

Features:
- MCP server that exposes n8n workflows as tools, resources, and prompts
- Custom n8n node for connecting to MCP servers from workflows
- Bidirectional bridge for data format conversion
- Token-based authentication and credential management
- Comprehensive error handling and logging
- Full test coverage for core components

Infrastructure:
- TypeScript/Node.js project setup with proper build configuration
- Docker support with multi-stage builds
- Development and production docker-compose configurations
- Installation script for n8n custom node deployment

Documentation:
- Detailed README with usage examples and API reference
- Environment configuration templates
- Troubleshooting guide

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

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

src/n8n/MCPApi.credentials.ts

@@ -0,0 +1,51 @@
+import {
+  ICredentialType,
+  INodeProperties,
+} from 'n8n-workflow';
+
+export class MCPApi implements ICredentialType {
+  name = 'mcpApi';
+  displayName = 'MCP API';
+  documentationUrl = 'mcp';
+  properties: INodeProperties[] = [
+    {
+      displayName: 'Server URL',
+      name: 'serverUrl',
+      type: 'string',
+      default: 'http://localhost:3000',
+      placeholder: 'http://localhost:3000',
+      description: 'The URL of the MCP server',
+    },
+    {
+      displayName: 'Authentication Token',
+      name: 'authToken',
+      type: 'string',
+      typeOptions: {
+        password: true,
+      },
+      default: '',
+      description: 'Authentication token for the MCP server (if required)',
+    },
+    {
+      displayName: 'Connection Type',
+      name: 'connectionType',
+      type: 'options',
+      options: [
+        {
+          name: 'HTTP',
+          value: 'http',
+        },
+        {
+          name: 'WebSocket',
+          value: 'websocket',
+        },
+        {
+          name: 'STDIO',
+          value: 'stdio',
+        },
+      ],
+      default: 'http',
+      description: 'How to connect to the MCP server',
+    },
+  ];
+}