Birthday was never saved (hydrate forced null) and not returned in a form the
clients use. Now:
- hydrate stores the incoming `birthday` (Unix) into date_of_birth; `birthday`
takes priority over a stray `date_of_birth: null` in the same payload so it
can't be wiped.
- toArray exposes a single `birthday` (Unix) key — drop the duplicate
`date_of_birth` output to avoid overlap.
- admin UserDetailPage reads profile.birthday (formatDate renders Jalali).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
