feat(edit): event editing — shared form, scoped recurring writes, recurrence picker (v1.3)

The create form (v1.2) now edits: a pencil on the detail screen (writable
calendars only, contextual WRITE upgrade like delete) opens it prefilled via
EventDetail.toEditForm; populated sections always show, the calendar is
fixed, and a dirty-check writes only changed columns (pristine saves are
no-ops). Saving a dirty recurring event parks in SaveUiState.AwaitingScope
and asks how far the change reaches (Google model): "only this event" =
modified-occurrence exception via CONTENT_EXCEPTION_URI (empty optionals as
explicit NULLs since the provider clones the parent row), "this and all
following" = series split (insert new event first, then truncate), "all
events" = series-row update with the time delta applied to the series
DTSTART. A changed rule drops the exception option. Delete gained the same
middle scope.

Recurrence: EventForm.rrule + SimpleRecurrence (FREQ/INTERVAL/UNTIL/COUNT +
weekly BYDAY with locale-ordered weekday toggles) behind a picker on create
and edit; unrepresentable rules render humanized (shared ui/common
RecurrenceText) and survive verbatim. UNTIL validation flags rules ending
before the event starts.

Provider lessons baked in (verified on-device via adb probes): instance
caches regenerate only from an update's own values, so truncation sends the
full time-column set (truncateSeries) — RRULE-only updates left a stale
duplicate occurrence on the split day; UNTIL is written as the local end of
day in UTC (toRRule(zone), previousLocalDayEndUtcMillis) so UTC+x zones
can't leak an extra day. Reminder edits reconcile against actual provider
rows, keeping untouched rows' methods.

Tests: RecurrenceTest (parse/render/round-trip, truncation), update/exception
mapper paths, repository pass-throughs, prefill + populatedFields, raw-title
mapper.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.planning/REQUIREMENTS.md

@@ -30,7 +30,10 @@ See full design spec: `docs/superpowers/specs/2026-06-08-calendar-app-design.md`
 - Home-screen widget
 - Full-text search
 - Quick-add
-- Custom notifications/reminders (system already handles these)
+- ~~Custom notifications/reminders (system already handles these)~~ —
+  **reversed:** Calendula targets sole-calendar-app users, so no other app
+  posts reminder notifications. We post them ourselves (Etar model). Planned
+  for v1.4 — see `ROADMAP.md`.
 - Tablet/foldable-specific layouts
 - iOS support (Android-only by design)