- Implement upsert (INSERT or UPDATE) logic for all reference table imports
- Fixed functions: import_trnstype, import_trnslkup, import_footers,
import_filestat, import_employee, import_gruplkup, import_filetype,
import_fvarlkup, import_rvarlkup
- Now checks if record exists before inserting; updates if exists
- Makes imports idempotent - can safely re-run without errors
- Added tracking of inserted vs updated counts in result dict
- Maintains batch commit performance for large imports
- Fixes sqlite3.IntegrityError when re-importing CSV files
