fix: add security headers and no-cache for index.html in nginx config

- X-Content-Type-Options, X-Frame-Options, Referrer-Policy, Permissions-Policy
- Prevent caching index.html so SPA updates are always picked up
- Add engines field (node >=18) and lint:fix script to package.json

package.json

@@ -30,7 +30,8 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "lint:fix": "eslint . --fix"
   },
   "dependencies": {
     "@radix-ui/react-collapsible": "^1.1.12",
@@ -63,5 +64,8 @@
     "typescript": "~5.9.3",
     "typescript-eslint": "^8.48.0",
     "vite": "^7.3.1"
+  },
+  "engines": {
+    "node": ">=18"
   }
 }