ver. 0.319: usunięcie shopPRO eksportu produktów + rozszerzenie API o custom_fields i security_information

- Usunięto shopproExportProduct() z IntegrationsRepository
- Usunięto shoppro_product_export() z IntegrationsController
- Usunięto przycisk "Eksportuj do shopPRO" z ShopProductController
- ProductRepository: dodano custom_fields i security_information do odpowiedzi API
- Zaktualizowano docs/API.md i testy

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

docs/API.md

@@ -237,7 +237,8 @@ Odpowiedz:
         "tab_description_1": null,
         "tab_name_2": null,
         "tab_description_2": null,
-        "canonical": null
+        "canonical": null,
+        "security_information": null
       }
     },
     "images": [
@@ -253,6 +254,9 @@ Odpowiedz:
         "value_names": {"pl": "Czerwony", "en": "Red"}
       }
     ],
+    "custom_fields": [
+      {"name": "Napis na koszulce", "type": "text", "is_required": 1}
+    ],
     "variants": [
       {
         "id": 101,