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/Support/AdminIntegrationSitePresenter.php

@@ -29,6 +29,7 @@ final class AdminIntegrationSitePresenter
             'wallet_api_key_masked' => is_string($site->wallet_api_key_encrypted) && $site->wallet_api_key_encrypted !== ''
                 ? '••••••••'
                 : null,
+            'is_default' => (bool) $site->is_default,
             'updated_at' => $site->updated_at?->toIso8601String(),
         ];
     }
@@ -38,16 +39,16 @@ final class AdminIntegrationSitePresenter
      */
     public static function detail(AdminSite $site): array
     {
-        return array_merge(self::listItem($site), [
+        return [
+            ...self::listItem($site),
             'wallet_debit_path' => (string) $site->wallet_debit_path,
             'wallet_credit_path' => (string) $site->wallet_credit_path,
             'wallet_balance_path' => (string) $site->wallet_balance_path,
             'iframe_allowed_origins' => $site->iframe_allowed_origins ?? [],
             'lottery_h5_base_url' => $site->lottery_h5_base_url,
             'notes' => $site->notes,
-            'is_default' => (bool) $site->is_default,
             'created_at' => $site->created_at?->toIso8601String(),
-        ]);
+        ];
     }
 
     /**