Wire client SignalrService to the live .NET backend

- @microsoft/signalr client implementing OnlineService: REST auth, hub
  matchmaking, server-driven game state (onState), play/trump, reactions;
  delegates not-yet-server-backed features (profile/friends/shop/chat/rooms)
  to the mock. Selected via NEXT_PUBLIC_USE_SERVER=1 (NEXT_PUBLIC_SERVER_URL)
- game-store live mode: enterServerMatch + applyServerState (maps server DTO,
  hides opponent hands, tally + SFX), inputs route to the hub; no local engine
- MatchmakingScreen auto-enters the live match when the server signals ready
- Verified end-to-end via scripts/live-test.mjs (auth -> hub -> match -> state)

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

package.json

@@ -9,6 +9,7 @@
     "lint": "eslint"
   },
   "dependencies": {
+    "@microsoft/signalr": "^10.0.0",
     "clsx": "^2.1.1",
     "framer-motion": "^12.40.0",
     "lucide-react": "^1.17.0",