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/utils/mcp-client.ts

@@ -0,0 +1,150 @@
+import { Client } from '@modelcontextprotocol/sdk/client/index.js';
+import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js';
+import { WebSocketClientTransport } from '@modelcontextprotocol/sdk/client/websocket.js';
+import {
+  CallToolRequest,
+  ListToolsRequest,
+  ListResourcesRequest,
+  ReadResourceRequest,
+  ListPromptsRequest,
+  GetPromptRequest,
+  CallToolResultSchema,
+  ListToolsResultSchema,
+  ListResourcesResultSchema,
+  ReadResourceResultSchema,
+  ListPromptsResultSchema,
+  GetPromptResultSchema,
+} from '@modelcontextprotocol/sdk/types.js';
+
+export interface MCPClientConfig {
+  serverUrl: string;
+  authToken?: string;
+  connectionType: 'http' | 'websocket' | 'stdio';
+}
+
+export class MCPClient {
+  private client: Client;
+  private config: MCPClientConfig;
+  private connected: boolean = false;
+
+  constructor(config: MCPClientConfig) {
+    this.config = config;
+    this.client = new Client(
+      {
+        name: 'n8n-mcp-client',
+        version: '1.0.0',
+      },
+      {
+        capabilities: {},
+      }
+    );
+  }
+
+  async connect(): Promise<void> {
+    if (this.connected) {
+      return;
+    }
+
+    let transport;
+    
+    switch (this.config.connectionType) {
+      case 'websocket':
+        const wsUrl = this.config.serverUrl.replace(/^http/, 'ws');
+        transport = new WebSocketClientTransport(new URL(wsUrl));
+        break;
+      
+      case 'stdio':
+        // For stdio, the serverUrl should be the command to execute
+        const [command, ...args] = this.config.serverUrl.split(' ');
+        transport = new StdioClientTransport({
+          command,
+          args,
+        });
+        break;
+      
+      default:
+        throw new Error(`HTTP transport is not yet supported for MCP clients`);
+    }
+
+    await this.client.connect(transport);
+    this.connected = true;
+  }
+
+  async disconnect(): Promise<void> {
+    if (this.connected) {
+      await this.client.close();
+      this.connected = false;
+    }
+  }
+
+  async listTools(): Promise<any> {
+    await this.ensureConnected();
+    return await this.client.request(
+      { method: 'tools/list' } as ListToolsRequest,
+      ListToolsResultSchema
+    );
+  }
+
+  async callTool(name: string, args: any): Promise<any> {
+    await this.ensureConnected();
+    return await this.client.request(
+      {
+        method: 'tools/call',
+        params: {
+          name,
+          arguments: args,
+        },
+      } as CallToolRequest,
+      CallToolResultSchema
+    );
+  }
+
+  async listResources(): Promise<any> {
+    await this.ensureConnected();
+    return await this.client.request(
+      { method: 'resources/list' } as ListResourcesRequest,
+      ListResourcesResultSchema
+    );
+  }
+
+  async readResource(uri: string): Promise<any> {
+    await this.ensureConnected();
+    return await this.client.request(
+      {
+        method: 'resources/read',
+        params: {
+          uri,
+        },
+      } as ReadResourceRequest,
+      ReadResourceResultSchema
+    );
+  }
+
+  async listPrompts(): Promise<any> {
+    await this.ensureConnected();
+    return await this.client.request(
+      { method: 'prompts/list' } as ListPromptsRequest,
+      ListPromptsResultSchema
+    );
+  }
+
+  async getPrompt(name: string, args?: any): Promise<any> {
+    await this.ensureConnected();
+    return await this.client.request(
+      {
+        method: 'prompts/get',
+        params: {
+          name,
+          arguments: args,
+        },
+      } as GetPromptRequest,
+      GetPromptResultSchema
+    );
+  }
+
+  private async ensureConnected(): Promise<void> {
+    if (!this.connected) {
+      await this.connect();
+    }
+  }
+}