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>

tests/bootstrap.php

@@ -50,6 +50,7 @@ if (!class_exists('S')) {
         public static function clear_redis_cache() {}
         public static function clear_product_cache($id) {}
         public static function send_email($to, $subject, $body) { return true; }
+        public static function remove_special_chars($str) { return str_ireplace(['\'', '"', ',', ';', '<', '>'], ' ', $str); }
     }
 }