Mirrors the frontend catch-up in 570f17e: a substantial amount of
finished-but-never-committed backend work had accumulated locally.
- New CustomField module: admin-managed field definitions per client,
reorderable, typed values stored per client (backing the frontend's
ClientCustomFieldCard + settings/fields page)
- History entries switch from a hardcoded type enum to a dynamic,
admin-managed HistoryType module (reorderable, backing
settings/history-types)
- New Import module: CSV client import (backing settings/import)
- Clients table gains soft deletes (deleted_at)
- Supporting factories, seeders, policies, and feature tests for all
of the above
All 63 backend tests pass locally before this commit.
