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.ShopTransport.php

@@ -2,12 +2,6 @@
 namespace front\factory;
 class ShopTransport
 {
-  // get_sellasist_transport_id
-  static public function get_sellasist_transport_id( $transport_method_id ) {
-    global $mdb;
-    return $mdb -> get( 'pp_shop_transports', 'sellasist_shipment_method_id', [ 'id' => $transport_method_id ] );
-  }
-
   // get_apilo_carrier_account_id
   static public function get_apilo_carrier_account_id( $transport_method_id )
   {