feat: 在 WalletBalanceController 中集成主站钱包余额获取功能

新增 HttpMainSiteWalletBalanceClient，用于在配置启用时获取主站钱包余额。
更新 WalletBalanceController：根据主站 API 返回结果新增 main_balance 与 main_balance_formatted 字段。
在 lottery.php 中新增钱包余额 API 路径配置项。
增强 WalletBalanceTest，验证在配置主站 API 后可正确获取 main_balance。

app/Http/Controllers/Api/V1/Wallet/WalletBalanceController.php

@@ -11,6 +11,7 @@ use App\Support\CurrencyResolver;
 use Illuminate\Http\JsonResponse;
 use App\Support\CurrencyFormatter;
 use App\Http\Controllers\Controller;
+use App\Services\Wallet\HttpMainSiteWalletBalanceClient;
 
 /**
  * 【玩家】查询彩票侧钱包余额。
@@ -22,12 +23,16 @@ use App\Http\Controllers\Controller;
  * - 币种：优先 Query `currency`，否则使用玩家 `default_currency`，再回退 `config('lottery.default_currency')`
  * - 若尚无 `player_wallets` 记录：按 `wallet_type=lottery` + 币种 **首次开立**一行（余额 0），便于新玩家直接进入查询
  * - `available_balance`：`balance - frozen_balance`，表示当前可用于下注的整数最小货币单位（不为负）
- * - `main_balance`：主站钱包余额占位，接入主站 API 后再返回实数；当前固定 `null`
+ * - `main_balance`：已配置 `MAIN_SITE_WALLET_API_URL` 时向主站查询；否则 `null`
  */
 final class WalletBalanceController extends Controller
 {
     private const WALLET_TYPE_LOTTERY = 'lottery';
 
+    public function __construct(
+        private readonly HttpMainSiteWalletBalanceClient $mainSiteBalanceClient,
+    ) {}
+
     public function __invoke(Request $request): JsonResponse
     {
         $player = $request->lotteryPlayer();
@@ -56,13 +61,17 @@ final class WalletBalanceController extends Controller
         $frozen = (int) $wallet->frozen_balance;
         $available = max(0, $balance - $frozen);
 
+        $mainBalance = $this->mainSiteBalanceClient->fetch($player, $currencyCode);
+
         return ApiResponse::success([
             'balance' => $balance,
             'balance_formatted' => CurrencyFormatter::fromMinor($balance),
             'available_balance' => $available,
             'available_balance_formatted' => CurrencyFormatter::fromMinor($available),
-            'main_balance' => null,
-            'main_balance_formatted' => null,
+            'main_balance' => $mainBalance,
+            'main_balance_formatted' => $mainBalance !== null
+                ? CurrencyFormatter::fromMinor($mainBalance)
+                : null,
             'currency_code' => $wallet->currency_code,
             'wallet_type' => $wallet->wallet_type,
             'frozen_balance' => $frozen,