ProPresenter export ignored service_songs.song_arrangement_id and
always used the default/is_default arrangement. Now the chosen
arrangement is pre-selected while ALL arrangements stay in the file,
so users can still switch in ProPresenter.
Import-stable, by NAME (avoids the fragile playlist arrangement UUID
that breaks on import):
- .pro: set selected_arrangement (protobuf field 10) to the chosen
arrangement via Song::setSelectedArrangementUuid(getArrangementByName).
- .proplaylist: set the presentation item arrangement_name (field 5).
buildGroups now emits the UNION of sections across all arrangements
(selected first, in play order, with first/last-slide macro anchoring;
other arrangements' sections appended without position macros) so every
arrangement's group-name refs resolve instead of being silently dropped.
No parser package changes; installed public API only. Library/no-service
context keeps default-arrangement behaviour unchanged.
