Full surface for create/get/list/rename/description/play_mode/kind/
delete/touch_play on collections and add/list/remove/reorder on items.
Dedup on exact (source, source_item_id) within a collection. Artist
collection kind is locked (cannot be converted to/from). Cascade
delete covers items. Position compaction on remove; atomic transaction
on reorder.
Covered by 10 unit tests using in-memory SQLite.
cc
vicrodh
c55a208215