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>

.env.example

@@ -51,4 +51,23 @@ AUTH_TOKEN=your-secure-token-here
 # CORS origin for HTTP mode (optional)
 # Default: * (allow all origins)
 # For production, set to your specific domain
-# CORS_ORIGIN=https://your-client-domain.com
+# CORS_ORIGIN=https://your-client-domain.com
+
+# =========================
+# N8N API CONFIGURATION
+# =========================
+# Optional: Enable n8n management tools by providing API credentials
+# These tools allow creating, updating, and executing workflows
+
+# n8n instance API URL (without /api/v1 suffix)
+# Example: https://your-n8n-instance.com
+# N8N_API_URL=
+
+# n8n API Key (get from Settings > API in your n8n instance)
+# N8N_API_KEY=
+
+# n8n API request timeout in milliseconds (default: 30000)
+# N8N_API_TIMEOUT=30000
+
+# Maximum number of API request retries (default: 3)
+# N8N_API_MAX_RETRIES=3