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/front/factory/class.ShopOrder.php

@@ -136,9 +136,7 @@ class ShopOrder
         'summary' => \S::normalize_decimal( $basket_summary + $transport_cost ),
         'coupon_id' => $coupon ? $coupon -> id : null,
         'message' => $basket_message ? $basket_message : null,
-        'baselinker_order_status_date' => date( 'Y-m-d H:i:s' ),
         'apilo_order_status_date' => date( 'Y-m-d H:i:s' ),
-        'sellasist_order_status_date' => date( 'Y-m-d H:i:s' ),
     ] );
 
     $order_id = $mdb -> id();