P14d: guest display names for players

- Players set a display name in the session panel ("Your name"); it persists
  (sessionStore.guestName) and is sent via a new `setName` message on join + edit.
- Server stores the name per connection and uses it in the roster + chat; the roster
  entry now also carries the player's character, so the GM sees "Alice · Lia".
- Realtime e2e: a player names themselves and the GM's roster/share update to match.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/index.ts

@@ -103,6 +103,7 @@ export function buildServer() {
           case 'gmRoll': hub.gmRoll(sender, m.gmSecret, m.label, m.expression, m.total, m.breakdown); break;
           case 'privateState': hub.privateState(sender, m.gmSecret, m.targetPlayerId, m.handout); break;
           case 'chat': hub.chat(sender, m.body, m.to); break;
+          case 'setName': hub.setName(sender, m.name); break;
         }
       });
       socket.on('close', () => { clearInterval(refill); hub.disconnect(sender); });