feat: integrate n8n management tools from n8n-manager-for-ai-agents (v2.6.0)

- Added 14 n8n management tools for workflow CRUD and execution management
- Integrated n8n API client with full error handling and validation
- Added conditional tool registration (only when N8N_API_URL configured)
- Complete workflow lifecycle: discover → build → validate → deploy → execute
- Updated documentation and added integration tests
- Maintains backward compatibility - existing functionality unchanged

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

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

src/utils/n8n-errors.ts

@@ -0,0 +1,136 @@
+import { logger } from './logger';
+
+// Custom error classes for n8n API operations
+
+export class N8nApiError extends Error {
+  constructor(
+    message: string,
+    public statusCode?: number,
+    public code?: string,
+    public details?: unknown
+  ) {
+    super(message);
+    this.name = 'N8nApiError';
+  }
+}
+
+export class N8nAuthenticationError extends N8nApiError {
+  constructor(message = 'Authentication failed') {
+    super(message, 401, 'AUTHENTICATION_ERROR');
+    this.name = 'N8nAuthenticationError';
+  }
+}
+
+export class N8nNotFoundError extends N8nApiError {
+  constructor(resource: string, id?: string) {
+    const message = id ? `${resource} with ID ${id} not found` : `${resource} not found`;
+    super(message, 404, 'NOT_FOUND');
+    this.name = 'N8nNotFoundError';
+  }
+}
+
+export class N8nValidationError extends N8nApiError {
+  constructor(message: string, details?: unknown) {
+    super(message, 400, 'VALIDATION_ERROR', details);
+    this.name = 'N8nValidationError';
+  }
+}
+
+export class N8nRateLimitError extends N8nApiError {
+  constructor(retryAfter?: number) {
+    const message = retryAfter
+      ? `Rate limit exceeded. Retry after ${retryAfter} seconds`
+      : 'Rate limit exceeded';
+    super(message, 429, 'RATE_LIMIT_ERROR', { retryAfter });
+    this.name = 'N8nRateLimitError';
+  }
+}
+
+export class N8nServerError extends N8nApiError {
+  constructor(message = 'Internal server error', statusCode = 500) {
+    super(message, statusCode, 'SERVER_ERROR');
+    this.name = 'N8nServerError';
+  }
+}
+
+// Error handling utility
+export function handleN8nApiError(error: unknown): N8nApiError {
+  if (error instanceof N8nApiError) {
+    return error;
+  }
+
+  if (error instanceof Error) {
+    // Check if it's an Axios error
+    const axiosError = error as any;
+    if (axiosError.response) {
+      const { status, data } = axiosError.response;
+      const message = data?.message || axiosError.message;
+
+      switch (status) {
+        case 401:
+          return new N8nAuthenticationError(message);
+        case 404:
+          return new N8nNotFoundError('Resource', message);
+        case 400:
+          return new N8nValidationError(message, data);
+        case 429:
+          const retryAfter = axiosError.response.headers['retry-after'];
+          return new N8nRateLimitError(retryAfter ? parseInt(retryAfter) : undefined);
+        default:
+          if (status >= 500) {
+            return new N8nServerError(message, status);
+          }
+          return new N8nApiError(message, status, 'API_ERROR', data);
+      }
+    } else if (axiosError.request) {
+      // Request was made but no response received
+      return new N8nApiError('No response from n8n server', undefined, 'NO_RESPONSE');
+    } else {
+      // Something happened in setting up the request
+      return new N8nApiError(axiosError.message, undefined, 'REQUEST_ERROR');
+    }
+  }
+
+  // Unknown error type
+  return new N8nApiError('Unknown error occurred', undefined, 'UNKNOWN_ERROR', error);
+}
+
+// Utility to extract user-friendly error messages
+export function getUserFriendlyErrorMessage(error: N8nApiError): string {
+  switch (error.code) {
+    case 'AUTHENTICATION_ERROR':
+      return 'Failed to authenticate with n8n. Please check your API key.';
+    case 'NOT_FOUND':
+      return error.message;
+    case 'VALIDATION_ERROR':
+      return `Invalid request: ${error.message}`;
+    case 'RATE_LIMIT_ERROR':
+      return 'Too many requests. Please wait a moment and try again.';
+    case 'NO_RESPONSE':
+      return 'Unable to connect to n8n. Please check the server URL and ensure n8n is running.';
+    case 'SERVER_ERROR':
+      return 'n8n server error. Please try again later or contact support.';
+    default:
+      return error.message || 'An unexpected error occurred';
+  }
+}
+
+// Log error with appropriate level
+export function logN8nError(error: N8nApiError, context?: string): void {
+  const errorInfo = {
+    name: error.name,
+    message: error.message,
+    code: error.code,
+    statusCode: error.statusCode,
+    details: error.details,
+    context,
+  };
+
+  if (error.statusCode && error.statusCode >= 500) {
+    logger.error('n8n API server error', errorInfo);
+  } else if (error.statusCode && error.statusCode >= 400) {
+    logger.warn('n8n API client error', errorInfo);
+  } else {
+    logger.error('n8n API error', errorInfo);
+  }
+}