feat(db): lot presentation + attachment sort order (schema v4→v5)

Expand LotType from {seed, plant} to six append-only forms (seed,
seedling, plant, tree, bulb, cutting) and add an optional Presentation
attribute (pot/tray/plug/bareRoot/rootBall) kept separate from quantity
so 'how many' and 'in what packaging' never conflate.

Add attachments.sortOrder so the cover photo is the lowest-ordered one,
enabling reordering from the full-screen viewer. Expand QuantityKind
with the new plant-aware forms.

Migrations are additive (v1→v5 all covered by migration_test); enum
values are stored by name and appended only, keeping CRDT sync safe.

apps/app_seeds/lib/state/variety_detail_cubit.dart

@@ -57,12 +57,14 @@ class VarietyDetailCubit extends Cubit<VarietyDetailState> {
     int? year,
     int? month,
     Quantity? quantity,
+    Presentation? presentation,
   }) => _repo.addLot(
     varietyId: varietyId,
     type: type,
     harvestYear: year,
     harvestMonth: month,
     quantity: quantity,
+    presentation: presentation,
   );
 
   Future<void> updateLot({
@@ -71,12 +73,14 @@ class VarietyDetailCubit extends Cubit<VarietyDetailState> {
     int? year,
     int? month,
     Quantity? quantity,
+    Presentation? presentation,
   }) => _repo.updateLot(
     lotId: lotId,
     type: type,
     harvestYear: year,
     harvestMonth: month,
     quantity: quantity,
+    presentation: presentation,
   );
 
   Future<void> deleteLot(String lotId) => _repo.softDeleteLot(lotId);
@@ -92,6 +96,9 @@ class VarietyDetailCubit extends Cubit<VarietyDetailState> {
   Future<void> removePhoto(String attachmentId) =>
       _repo.removePhoto(attachmentId);
 
+  Future<void> setPreferredPhoto(String attachmentId) =>
+      _repo.setPreferredPhoto(varietyId, attachmentId);
+
   Future<void> addExternalLink(String url, {String? title}) =>
       _repo.addExternalLink(varietyId, url, title: title);