fix(calendars): make the Settings toggle the one visibility model (#75)

Reminders never fired for a calendar hidden at system level and nothing hinted
at it: the provider only schedules reminder alarms for Calendars.VISIBLE=1,
while Calendula filtered with its own disabledCalendarIds pref and parsed
isVisibleInSystem without ever using it — two models that could disagree
indefinitely.

Settings → Calendars now writes Calendars.VISIBLE, one calendar per update
(CalendarProvider2 skips its own checkNextAlarm() reschedule for any selection
that isn't _id=), and every display predicate reads isVisibleInSystem. The
drawer's filter sheet stays a purely in-app declutter and still leaves reminders
alone.

With VISIBLE=0 the provider creates no alert rows, so there is nothing left to
suppress: the disabled-calendar gates, SuppressedReminderStore and the re-enable
recovery are gone. A one-shot migration reconciles the retired set with the app's
state winning — enabled in-app and syncing gets shown, disabled gets hidden,
everything else untouched — so the upgrade changes nothing the user sees.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,21 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+- Reminders now arrive for every calendar you have switched on. A calendar that
+  was hidden at system level — switched off in another calendar app, or never
+  switched on after being added — still showed its events and listed their
+  reminders in Calendula, but never notified: Android only schedules reminder
+  alarms for calendars marked visible, and Calendula kept its own separate
+  on/off list that had no say in it. There is now one switch: **Settings →
+  Calendars** turns a calendar on or off for the whole device, so what you see
+  and what reminds you can no longer disagree. Your current selection is carried
+  over on first launch, and calendars whose events aren't stored on this device
+  are left as they are ([#75]).
+
+  The drawer's filter is unchanged and still app-only: hiding a calendar there
+  tidies your view without silencing its reminders.
+
 ## [2.16.0] — 2026-07-24
 
 ### Added
@@ -1112,3 +1127,4 @@ automatically, with zero telemetry and no internet permission.
 [#42]: https://codeberg.org/jlmakiola/calendula/issues/42
 [#44]: https://codeberg.org/jlmakiola/calendula/issues/44
 [#70]: https://codeberg.org/jlmakiola/calendula/issues/70
+[#75]: https://codeberg.org/jlmakiola/calendula/issues/75