feat(games): implement blackjack game plugin with manual start and custom payouts

Adds a full blackjack game with dealer AI, hit/stand/double-down actions,
and per-player payout multipliers (house-edge model). Extends the game
framework with manualStart support and a START_GAME WebSocket message so
hosts can begin when ready. Generalizes bet settlement transaction
descriptions from chess-specific to game-agnostic.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

panel/src/lib/useGameRoom.ts

@@ -171,5 +171,9 @@ export function useGameRoom(roomId: string, userId: string, role?: string, prefe
         send({ type: "FILL_ROOM", roomId });
     }, [roomId, send]);
 
-    return { ...state, sendAction, leaveRoom, rejoin, fillRoom };
+    const startGame = useCallback(() => {
+        send({ type: "START_GAME", roomId });
+    }, [roomId, send]);
+
+    return { ...state, sendAction, leaveRoom, rejoin, fillRoom, startGame };
 }