docs: add API security hardening design plan

Security improvements identified for the protect-api-with-api-key branch:
- Use short-lived wsToken for WebSocket auth (not session tokens in URLs)
- Add AUTOMAKER_HIDE_API_KEY env var to suppress console logging
- Add rate limiting to login endpoint (5 attempts/min/IP)
- Use timing-safe comparison for API key validation
- Make WebSocket tokens single-use

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/server/package.json

@@ -38,6 +38,7 @@
     "ws": "^8.18.3"
   },
   "devDependencies": {
+    "@types/cookie": "^0.6.0",
     "@types/cookie-parser": "^1.4.10",
     "@types/cors": "^2.8.19",
     "@types/express": "^5.0.6",