feat: implement security audit fixes - rate limiting and SSRF protection (Issue #265 PR #2)

This commit implements HIGH-02 (Rate Limiting) and HIGH-03 (SSRF Protection)
from the security audit, protecting against brute force attacks and
Server-Side Request Forgery.

Security Enhancements:
- Rate limiting: 20 attempts per 15 minutes per IP (configurable)
- SSRF protection: Three security modes (strict/moderate/permissive)
- DNS rebinding prevention
- Cloud metadata blocking in all modes

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

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

README.md

@@ -198,10 +198,36 @@ Add to Claude Desktop config:
 }
 ```
 
->💡 Tip: If you’re running n8n locally on the same machine (e.g., via Docker), use http://host.docker.internal:5678 as the N8N_API_URL.
+>💡 Tip: If you're running n8n locally on the same machine (e.g., via Docker), use http://host.docker.internal:5678 as the N8N_API_URL.
 
 > **Note**: The n8n API credentials are optional. Without them, you'll have access to all documentation and validation tools. With them, you'll additionally get workflow management capabilities (create, update, execute workflows).
 
+### 🏠 Local n8n Instance Configuration
+
+If you're running n8n locally (e.g., `http://localhost:5678` or Docker), you need to allow localhost webhooks:
+
+```json
+{
+  "mcpServers": {
+    "n8n-mcp": {
+      "command": "docker",
+      "args": [
+        "run", "-i", "--rm", "--init",
+        "-e", "MCP_MODE=stdio",
+        "-e", "LOG_LEVEL=error",
+        "-e", "DISABLE_CONSOLE_OUTPUT=true",
+        "-e", "N8N_API_URL=http://host.docker.internal:5678",
+        "-e", "N8N_API_KEY=your-api-key",
+        "-e", "WEBHOOK_SECURITY_MODE=moderate",
+        "ghcr.io/czlonkowski/n8n-mcp:latest"
+      ]
+    }
+  }
+}
+```
+
+> ⚠️ **Important:** Set `WEBHOOK_SECURITY_MODE=moderate` to allow webhooks to your local n8n instance. This is safe for local development while still blocking private networks and cloud metadata.
+
 **Important:** The `-i` flag is required for MCP stdio communication.
 
 > 🔧 If you encounter any issues with Docker, check our [Docker Troubleshooting Guide](./docs/DOCKER_TROUBLESHOOTING.md).