Integrations DI refactor, remove Sellasist/Baselinker, fix product-edit encoding (0.263)

- New: Domain\Integrations\IntegrationsRepository + admin\Controllers\IntegrationsController (DI)
- Cleanup: removed all Sellasist and Baselinker integrations from entire project
- Fix: product-edit.php Polish characters (UTF-8/CP1250 double-encoding)
- Update: factory\Integrations as facade (Apilo + ShopPRO only)
- Tests: 212 tests, 577 assertions

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

autoload/admin/controls/class.ShopPaymentMethod.php

@@ -6,7 +6,6 @@ class ShopPaymentMethod
   {
     return \Tpl::view( 'shop-payment-method/view-list', [
       'apilo_payment_types_list' => unserialize( \admin\factory\Integrations::apilo_settings( 'payment-types-list' ) ),
-      'sellasist_payment_types_list' => unserialize( \admin\factory\Integrations::sellasist_settings( 'payment_types_list' ) ),
     ] );
   }
 }