feat: refactor super admin to use is_super_admin flag and enhance site deletion logic

- Changed super admin detection from role-based to `is_super_admin` flag in AdminUser model
- Added `requireDefaultAdminSiteId()` method to throw validation error when no integration site exists
- Enhanced site deletion to migrate platform role bindings to fallback site and auto-delete site-specific admin accounts
- Made agent line code optional with auto-generation fallback using `{site_code}-agent-{counter}` format

app/Http/Controllers/Api/V1/Admin/Integration/AdminIntegrationSiteDestroyController.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1\Admin\Integration;
+
+use App\Models\AdminSite;
+use App\Support\ApiMessage;
+use App\Support\ApiResponse;
+use App\Lottery\ErrorCode;
+use Illuminate\Http\Request;
+use Illuminate\Http\JsonResponse;
+use App\Http\Controllers\Controller;
+use App\Services\AuditLogger;
+use App\Services\Integration\IntegrationSiteService;
+use App\Support\AdminIntegrationSiteAccess;
+use App\Support\AdminIntegrationSitePresenter;
+use App\Http\Middleware\RecordAdminApiAudit;
+
+final class AdminIntegrationSiteDestroyController extends Controller
+{
+    public function __invoke(
+        Request $request,
+        AdminSite $admin_site,
+        IntegrationSiteService $service,
+    ): JsonResponse {
+        $admin = $request->lotteryAdmin();
+        abort_if($admin === null, 401);
+
+        if (! AdminIntegrationSiteAccess::canAccess($admin, $admin_site)) {
+            return ApiMessage::errorResponse($request, 'admin.site_delete_denied', ErrorCode::AdminForbidden->value, null, 403);
+        }
+
+        $before = AdminIntegrationSitePresenter::detail($admin_site);
+        $service->destroy($admin_site);
+
+        AuditLogger::recordForAdmin(
+            $admin,
+            $request,
+            moduleCode: 'integration',
+            actionCode: 'destroy',
+            targetType: 'admin_site',
+            targetId: (string) $before['id'],
+            beforeJson: $before,
+            afterJson: null,
+        );
+        $request->attributes->set(RecordAdminApiAudit::ATTRIBUTE_AUDIT_RECORDED, true);
+
+        return ApiResponse::success(null);
+    }
+}