Apply settings changes at their save time and retry failed claims

A settings change is now queued with the instant it was saved, and the
loop handles fire times up to that instant under the old rule and later
ones under the new, so a fire time the change made due is not skipped
when the scheduler gets to the change late (SCHED-01).

A failed claim no longer advances the loop past its period: the pass is
repeated every ClaimRetry until the claim succeeds, and periods already
claimed in that pass are skipped by the claim, so each runs once
(SCHED-02).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -793,7 +793,11 @@ key (`Rule.PeriodKey`): the local date for a daily rule, the ISO week of the
 fire date for a weekly one, or of the week after for `WeeklyForNextWeek`
 (`plan_draft`). Inserting `schedule_runs(schedule, period_key)` is the claim;
 a period already claimed is skipped, so a period runs at most once and a
-failed run is not retried. At boot only each schedule's most recent fire
+failed run is not retried. A claim that fails is not skipped: the pass is
+repeated every `scheduler.ClaimRetry` until the claim succeeds. A settings
+change is recorded with the instant it was saved, and fire times up to that
+instant follow the old rule and later ones the new, however late the
+scheduler applies it. At boot only each schedule's most recent fire
 time is considered: it runs if it passed within 24 hours, and is otherwise
 claimed without running (logged as missed) so it never runs later. DST
 follows `household.LocalTime`: a skipped time fires later by the gap, a