Group lookups (createNodeIfNeeded, findCardNode) must not resolve a
mirrored custom zone that shares the group name. Introduce
findGroupChild to search only non-custom children, and make addCard
consult the deck tree before falling back to creating a top-level zone
so cards added to an un-mirrored custom zone land inside it.
mirrorCustomZones now flattens cards nested at any depth into the
mirrored zone so no card is left without a model row.
Add model behaviour tests (addCard routing, same-name group/zone
collision, removeRows guard, empty-zone survival, findCard inside a
custom zone) and fix the missing main() in the unit test binaries.
DeckListModel now surfaces the custom zones from the deck tree so
views can render and edit them alongside criteria groups.
The custom-zone bookkeeping that made the model unwieldy is extracted
into DeckListModelCustomZones (deck_list_model_custom_zones.h/.cpp), a
single self-contained unit owning every "what is / where is a custom
zone" decision for the model's shadow tree:
- rebuildTree mirrors each custom zone as a DecklistModelSubZoneNode
under its board zone, cards flat inside (no further grouping).
- The freshly built shadow tree is sorted while the model reset is
still open, so views never observe unsorted intermediate order and
proxies cannot desync.
- Custom zones always sort after criteria groups within a board,
regardless of their names. One shared sortWithCustomZonesLast backs
both the live sortHelper (which remaps persistent indexes from the
movement mapping) and the silent reset-time sortShadowTree.
- addCard inserts flat into a custom zone by name and keeps grouping
by active criteria for board zones. findCardNode resolves cards in
both layouts, legacy top-level zones unchanged.
- New IsCustomZoneRole lets views tell zones apart from groups.
- Empty custom zones survive row removal. Zone rows themselves are
only mutable through the deck tree API.
A new deck_list_model_custom_zones_test suite locks the extracted
shadow-tree logic (type testing, mirroring, name lookup, and the
sort-with-custom-zones-last mapping).
No behavior change.
