feat(edit): move an event to another calendar (#39)

The calendar row in the editor is now tappable when editing an existing
event: picking a different calendar moves the event there on save, rather
than forcing a delete-and-recreate.

CALENDAR_ID is sync-adapter-owned and can't be updated in place, so the
move is copy+delete: the master row is re-inserted on the target calendar
(preserving UID_2445 so backup dedup and sync identity survive), its
reminders and editable guests are copied, and — for a recurring series —
every exception is replayed against the new master (modified occurrences
via CONTENT_EXCEPTION_URI, cancellations as STATUS_CANCELED). The user's
field edits are then applied with the normal series update. Everything on
the new side is built before the source is deleted (post-before-delete),
with a rollback of the copy on any failure, so a move is all-or-nothing.

A calendar change forces whole-series scope, so it skips the recurring
scope dialog. Managed special-dates calendars stay locked. Colour is not
carried across (a raw/keyed colour may be invalid on the target account),
matching the existing calendar-switch behaviour.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,18 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+- Move an event to another calendar. When editing an existing event, the
+  calendar row is now tappable — pick a different calendar and saving moves the
+  event across, instead of having to delete it and recreate it elsewhere.
+  Recurring series move as a whole, keeping their individually-edited and
+  cancelled occurrences, and any reminders and guests come along too. A calendar
+  can't simply be reassigned underneath an event, so Calendula recreates it on
+  the target and removes the original — the same approach other calendar apps
+  take. Thanks to @prismplex for the suggestion ([#39]).
+
 ## [2.14.0] — 2026-07-06
 
 ### Added
@@ -874,3 +886,4 @@ automatically, with zero telemetry and no internet permission.
 [#33]: https://codeberg.org/jlmakiola/calendula/issues/33
 [#34]: https://codeberg.org/jlmakiola/calendula/issues/34
 [#37]: https://codeberg.org/jlmakiola/calendula/issues/37
+[#39]: https://codeberg.org/jlmakiola/calendula/issues/39