- Introduced SaleAbstractModel and SaleLineAbstractModel as abstract bases
- Added CatalogSale and CatalogSaleLine models inheriting from them
- Created migration 0045 for new models
- Added CatalogSaleView, CatalogSaleSerializer with nested line creation
- Registered new models in admin
- Added catalog_sales router endpoint to URLs
- Removed placeholder api/ package (now redundant)
- Split monolithic models.py into models/ package (customers, products, sales, payments, admin)
- Removed forms.py, all HTML templates, and associated template-based views
- Added api/ package with CatalogSaleView placeholder
- Updated all imports across project to use new model paths
- Removed obsolete tests (form, export, purchase, summary tests)
- Removed template-based URL patterns, kept only API endpoints
- Standardized string quotes (single to double) and reformatted code
