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>

package.runtime.json

@@ -1,12 +1,13 @@
 {
   "name": "n8n-mcp-runtime",
-  "version": "2.16.1",
+  "version": "2.16.3",
   "description": "n8n MCP Server Runtime Dependencies Only",
   "private": true,
   "dependencies": {
     "@modelcontextprotocol/sdk": "^1.13.2",
     "@supabase/supabase-js": "^2.57.4",
     "express": "^5.1.0",
+    "express-rate-limit": "^7.1.5",
     "dotenv": "^16.5.0",
     "lru-cache": "^11.2.1",
     "sql.js": "^1.13.0",