server/server.js — added helmet with CSP configured to allow Google Fonts

Dockerfile — creates a non-root app user and runs the process under it
server/routes.js — tailscale_ip validated against IPv4 regex (empty string still allowed)
index.html — sql.js CDN script tag already removed earlier in this session

package.json

@@ -1,6 +1,6 @@
 {
   "name": "catalyst",
-  "version": "1.1.0",
+  "version": "1.1.1",
   "type": "module",
   "scripts": {
     "start": "node server/server.js",
@@ -9,7 +9,8 @@
     "version:write": "node -e \"const {version}=JSON.parse(require('fs').readFileSync('package.json','utf8'));require('fs').writeFileSync('js/version.js','const VERSION = \\\"'+version+'\\\";\\n');\""
   },
   "dependencies": {
-    "express": "^4.18.0"
+    "express": "^4.18.0",
+    "helmet": "^8.1.0"
   },
   "devDependencies": {
     "jsdom": "^25.0.0",