Add run_webhook tool for executing workflows via webhooks

This commit adds a new MCP tool, run_webhook, which allows executing n8n workflows via webhooks instead of using the API directly. This implementation:

1. Creates a new RunWebhookHandler class that:
   - Takes a workflowName parameter and automatically prepends "webhook/" to create the full path
   - Uses basic authentication from environment variables
   - Makes HTTP requests to the webhook endpoints and returns the responses

2. Adds new environment variables:
   - N8N_WEBHOOK_USERNAME: Username for webhook basic authentication
   - N8N_WEBHOOK_PASSWORD: Password for webhook basic authentication

3. Updates server configuration and handlers to register and expose the new tool

4. Adds comprehensive documentation in:
   - execution-tools.md with examples and schema
   - README.md with configuration and usage information

This provides a simpler alternative to the API-based workflow execution, allowing Claude to trigger n8n webhooks directly.

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

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

src/config/server.ts

@@ -110,7 +110,8 @@ function setupToolCallRequestHandler(server: Server): void {
       const {
         ListExecutionsHandler,
         GetExecutionHandler,
-        DeleteExecutionHandler
+        DeleteExecutionHandler,
+        RunWebhookHandler
       } = await import('../tools/execution/index.js');
       
       // Route the tool call to the appropriate handler
@@ -144,6 +145,9 @@ function setupToolCallRequestHandler(server: Server): void {
       } else if (toolName === 'delete_execution') {
         const handler = new DeleteExecutionHandler();
         result = await handler.execute(args);
+      } else if (toolName === 'run_webhook') {
+        const handler = new RunWebhookHandler();
+        result = await handler.execute(args);
       } else {
         throw new Error(`Unknown tool: ${toolName}`);
       }