- Add comprehensive test suite for CSV import in ItemsCsvImportTest.php
- Test CSV header generation (locations, attributes, BOM handling)
- Test CSV file parsing (multiple rows, BOM detection)
- Test item import (basic fields, quantities, inventory records)
- Test item updates, taxes, and attributes
- Test edge cases (zero quantities, negative values, precision)
- Add GitHub Actions workflow for unit tests
- Tests verify data ends up correctly in items/item_quantities tables
