AttendanceLogForm.clean only checked end >= start — a typo'd year in
the end-date field created a WorkLog per worker per day for the whole
span (365+ days) in one submit, with no way back but manual deletion.
Ranges longer than 31 days (a full calendar month) are now rejected
with a message pointing at the year fields.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>