fix: Correct PnL calculation to show net profit instead of gross payout

- GameServer.ts: Calculate netProfit = grossPayout - betAmount and send as 'net'
  instead of sending gross payout labeled as net
- BlackjackGame.tsx: Fix PnL calculations to use net profit correctly
  - Hand win/blackjack now shows net profit (payout minus bet)
  - Lose correctly shows negative bet amount
  - Round result banner displays roundNet (net profit) with appropriate colors
- Remove dead code (myPnl variable that was calculated but never used)
- Update color coding: green for profit, red for loss, blue for zero balance

api/src/games/GameServer.ts

@@ -97,15 +97,16 @@ export class GameServer {
 
             for (const [playerId, multiplier] of Object.entries(roundPayouts)) {
                 if (multiplier <= 0) continue;
-                const amount = Math.floor(betAmount * multiplier);
+                const grossPayout = Math.floor(betAmount * multiplier);
+                const netProfit = grossPayout - betAmount; // Calculate net profit (gross payout minus original bet)
                 try {
                     await economyService.modifyUserBalance(
                         playerId,
-                        BigInt(amount),
+                        BigInt(grossPayout),
                         TransactionType.GAME_WIN,
                         `${gameName} round payout (room ${roomId.slice(0, 8)})`,
                     );
-                    payoutDetails[playerId] = { net: amount };
+                    payoutDetails[playerId] = { net: netProfit };
                 } catch (err) {
                     logger.error("web", `Round payout failed for ${playerId} in room ${roomId}: ${err}`);
                 }