feat(block1): variety detail + edit screen with reactive lots

Tapping an inventory item now opens its detail (the /variety/:id route was a
placeholder). Read + edit one variety end-to-end:

- Detail view: photo, category, "also known as" names, notes and lots, driven
  by a reactive VarietyDetailCubit.
- Edit core fields (label/category/notes, LWW) via a bottom sheet.
- Add a lot (harvest year + quantity) — the list refreshes reactively.
- Soft-delete (tombstone) with a confirm dialog.

Repository:
- watchVariety(id): merges Drift table-change streams (variety, lots, names,
  attachments) via StreamGroup and reloads the full detail on any change, so a
  lot added to a *different* table still refreshes the view.
- updateVariety (LWW), addLot, softDeleteVariety.

i18n: detail/edit/addLot strings (ES/EN); switched slang to {param} braces
interpolation (translator- and Weblate-friendly).

Tests: repository (reactive watchVariety, update, soft-delete) and widget tests
(render, edit updates title, add-lot appears, delete shows not-found). Full
suite green: 23 passing, 1 skipped (SQLCipher-only encryption guard).

apps/app_seeds/lib/state/variety_detail_cubit.dart

@@ -0,0 +1,68 @@
+import 'dart:async';
+
+import 'package:commons_core/commons_core.dart';
+import 'package:equatable/equatable.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+
+import '../data/variety_repository.dart';
+
+class VarietyDetailState extends Equatable {
+  const VarietyDetailState({
+    this.detail,
+    this.loading = true,
+    this.deleted = false,
+  });
+
+  final VarietyDetail? detail;
+  final bool loading;
+  final bool deleted;
+
+  @override
+  List<Object?> get props => [detail, loading, deleted];
+}
+
+/// Streams one variety's detail and edits it through the repository.
+class VarietyDetailCubit extends Cubit<VarietyDetailState> {
+  VarietyDetailCubit(this._repo, this.varietyId)
+    : super(const VarietyDetailState()) {
+    _sub = _repo
+        .watchVariety(varietyId)
+        .listen(
+          (d) => emit(
+            VarietyDetailState(
+              detail: d,
+              loading: false,
+              deleted: state.deleted,
+            ),
+          ),
+        );
+  }
+
+  final VarietyRepository _repo;
+  final String varietyId;
+  late final StreamSubscription<VarietyDetail?> _sub;
+
+  Future<void> updateFields({String? label, String? category, String? notes}) =>
+      _repo.updateVariety(
+        id: varietyId,
+        label: label,
+        category: category,
+        notes: notes,
+      );
+
+  Future<void> addLot({int? year, Quantity? quantity}) =>
+      _repo.addLot(varietyId: varietyId, harvestYear: year, quantity: quantity);
+
+  Future<void> deleteVariety() async {
+    await _repo.softDeleteVariety(varietyId);
+    emit(
+      VarietyDetailState(detail: state.detail, loading: false, deleted: true),
+    );
+  }
+
+  @override
+  Future<void> close() async {
+    await _sub.cancel();
+    return super.close();
+  }
+}