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/class.Site.php

@@ -311,6 +311,13 @@ class Site
           new \Domain\Layouts\LayoutsRepository( $mdb )
         );
       },
+      'Integrations' => function() {
+        global $mdb;
+
+        return new \admin\Controllers\IntegrationsController(
+          new \Domain\Integrations\IntegrationsRepository( $mdb )
+        );
+      },
     ];
 
     return self::$newControllers;