ReminderOverride.Minutes now carries a List<Int> of lead times so a target
can hold several reminders at once; an app that offers a single reminder uses a
one-element list. Map helpers move to Map<Long, List<Int>> (empty list = explicit
None), and the codec gains a third (list) separator while single legacy values
round-trip byte-identically. Adds reminderOverrideForMinutes/normalizeReminders/
reminderLeadsFor. Upstreamed from Calendula's per-calendar multi-reminders.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Pure-Kotlin module, drawn from the duplicate reminder logic in Agendula and
Calendula: the lead-time unit model (ReminderUnit / decomposeReminderMinutes),
the per-target override model (ReminderOverride + reminderLeadFor /
applyReminderOverride) and the stored-format codec (ReminderOverrideCodec).
The codec's separators are configurable so each app keeps its on-disk format
(Agendula stores id:minutes, Calendula id=minutes) without a data migration.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
