Refactor model imports and update admin classes to use pghistory for historical tracking; replace HistoricalModel with TrackedModel in relevant models

designers/admin.py

@@ -1,10 +1,13 @@
 from django.contrib import admin
-from simple_history.admin import SimpleHistoryAdmin
+from django.utils.text import slugify
 from .models import Designer
 
 @admin.register(Designer)
-class DesignerAdmin(SimpleHistoryAdmin):
+class DesignerAdmin(admin.ModelAdmin):
     list_display = ('name', 'headquarters', 'founded_date', 'website')
     search_fields = ('name', 'headquarters')
-    list_filter = ('founded_date',)
     prepopulated_fields = {'slug': ('name',)}
+    readonly_fields = ('created_at', 'updated_at')
+
+    def get_queryset(self, request):
+        return super().get_queryset(request).select_related()