Show app version in lobby footer; expose version via /api/config

- Server reads version from package.json and returns it from /api/config
- Client fetches it at boot and renders it in a lobby footer
- Bump service-worker cache to shelem-v3 so precache refreshes

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "shelem",
-  "version": "1.0.0",
+  "version": "1.1.2",
   "description": "Shelem card game — multiplayer",
   "main": "server.js",
   "scripts": {