Add choices API endpoint and OpenAPI client setup

Introduces a new /api/choices/ endpoint for fetching model choices with multilingual labels. Updates Django models to use 'cz#' prefix for Czech labels. Adds OpenAPI client generation via orval, refactors frontend API structure, and provides documentation and helper scripts for dynamic choices and OpenAPI usage.

backend/vontor_cz/urls.py

@@ -16,6 +16,7 @@ Including another URLconf
 """
 from django.contrib import admin
 from django.urls import path, include
+from .views import choices
 
 from drf_spectacular.views import (
     SpectacularAPIView,
@@ -31,6 +32,7 @@ urlpatterns = [
 
 
     path('admin/', admin.site.urls),
+    path("api/choices/", choices, name="choices"),
     path('api/account/', include('account.urls')),
     path('api/commerce/', include('commerce.urls')),
     #path('api/advertisments/', include('advertisements.urls')),