Issue #8: Inconsistent naming for model-to-response conversion functions.
Changes:
- Rename build_invite_response to _to_invite_response (invites.py)
- Rename _map_counter_record to _to_counter_record_response (audit.py)
- Rename _map_sum_record to _to_sum_record_response (audit.py)
All conversion functions now follow the _to_X_response pattern,
using underscore prefix for module-private functions.