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/test/data/variety_detail_test.dart

@@ -171,4 +171,17 @@ void main() {
 
     expect((await repo.watchVariety(id).first)!.lots, isEmpty);
   });
+
+  test('add and remove vernacular names', () async {
+    final id = await repo.addQuickVariety(label: 'Maize');
+    final nameId = await repo.addVernacularName(id, 'Maíz');
+
+    expect(
+      (await repo.watchVariety(id).first)!.vernacularNames.map((n) => n.name),
+      ['Maíz'],
+    );
+
+    await repo.removeVernacularName(nameId);
+    expect((await repo.watchVariety(id).first)!.vernacularNames, isEmpty);
+  });
 }