Security hardening: escape names in result screens, drop tech-stack headers

- Escape player names rendered via innerHTML on the hand-over and game-over
  score rows (defense-in-depth XSS; names are already capped at 16 chars)
- app.disable('x-powered-by') to stop advertising Express
- Add safe response headers: X-Content-Type-Options, X-Frame-Options,
  Referrer-Policy (no CSP — inline SW script + socket.io would need unsafe-inline)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "shelem",
-  "version": "1.1.6",
+  "version": "1.1.7",
   "description": "Shelem card game — multiplayer",
   "main": "server.js",
   "scripts": {