feat(inventory): editable vernacular (common) names

The "also known as" names were read-only; now they can be added and removed:
- Repository: addVernacularName + removeVernacularName (soft delete);
  VarietyDetail.vernacularNames carries ids (new VernacularName model).
- Cubit: addVernacularName / removeVernacularName.
- Detail: deletable name chips + an "Add name" chip opening a small dialog;
  the section is always visible so names can be added when empty.

Tests: repo add/remove + widget add/remove. 44 green.

apps/app_seeds/lib/state/variety_detail_cubit.dart

@@ -76,6 +76,12 @@ class VarietyDetailCubit extends Cubit<VarietyDetailState> {
 
   Future<void> deleteLot(String lotId) => _repo.softDeleteLot(lotId);
 
+  Future<void> addVernacularName(String name) =>
+      _repo.addVernacularName(varietyId, name);
+
+  Future<void> removeVernacularName(String nameId) =>
+      _repo.removeVernacularName(nameId);
+
   Future<void> linkSpecies(String speciesId) =>
       _repo.linkSpecies(varietyId, speciesId);