Describe presence_patterns (zero or more home/away patterns per child,
each with its own cycle length and anchor date), the first-match-wins
evaluation order, and migration 9 replacing the one-per-child schedule
table. Update the Admin Schedule spec for the patterns list, pattern
editor, combined month grid and Sunday-first week; replace the
set_presence_pattern service row with the admin pattern routes; and add
the pre-upgrade backup and rollback step for migration 9 to the runbook.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>