- Added FastAPI views for supplier invoices in the billing frontend.
- Created EconomicService for handling e-conomic API interactions, including safety modes for read-only and dry-run operations.
- Developed database migration for supplier invoices, including tables for invoices, line items, and settings.
- Documented kassekladde module features, architecture, API endpoints, and usage guide in KASSEKLADDE.md.
- Implemented views for overdue invoices and pending e-conomic sync.
