#51 feat: registrar categorias en admin y documentar endpoints

Issue #51: discriminacion y administracion de categorias de productos.

- ProductCategoryAdmin con list_display/filtro por active
- doc/requests.org: GET/PATCH product_categories, import_from_external,
  deactivate, activate

tienda_ilusion/don_confiao/admin.py

@@ -77,6 +77,12 @@ class ProductAdmin(admin.ModelAdmin):
     search_fields = ("id", "name",)
     list_filter = ("name", "id")
 
-admin.site.register(ProductCategory)
+
+@admin.register(ProductCategory)
+class ProductCategoryAdmin(admin.ModelAdmin):
+    list_display = ("id", "name", "alternative_name", "active", "external_id")
+    search_fields = ("name", "alternative_name", "external_id")
+    list_filter = ("active",)
+
 admin.site.register(Payment)
 admin.site.register(ReconciliationJar)