refactor: 迁移彩票设置至 LotterySettings 服务

- 更新多个控制器和服务，使用 LotterySettings 服务获取彩票相关配置，如默认币种、开奖间隔、下注窗口等，提升代码一致性与可维护性。
- 移除 .env.example 中不再使用的配置项，建议通过后台管理进行设置。

app/Http/Controllers/Api/V1/Admin/Currency/AdminCurrencyDestroyController.php

@@ -7,6 +7,7 @@ use App\Lottery\ErrorCode;
 use App\Support\ApiResponse;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Support\Facades\DB;
+use App\Services\LotterySettings;
 use App\Http\Controllers\Controller;
 
 final class AdminCurrencyDestroyController extends Controller
@@ -15,7 +16,7 @@ final class AdminCurrencyDestroyController extends Controller
     {
         $code = strtoupper((string) $currency->code);
 
-        if ($code === strtoupper((string) config('lottery.default_currency', 'NPR'))) {
+        if ($code === LotterySettings::defaultCurrency()) {
             return ApiResponse::error(
                 '默认币种不可删除',
                 ErrorCode::ValidationFailed->value,