feat(inventory): edit and delete existing lots

Lots could only be created; now they can be edited and removed:
- Repository: updateLot (LWW) + softDeleteLot (tombstone).
- Cubit: updateLot / deleteLot.
- The add-lot sheet is now a shared add/edit sheet — tapping a lot opens it
  prefilled (type, year, quantity), with a trash action to delete. The reactive
  detail view refreshes on save/delete.

Tests: repo updateLot/softDeleteLot + widget edit-lot and delete-lot. 42 green.

apps/app_seeds/lib/ui/variety_detail_screen.dart

@@ -1,4 +1,3 @@
-import 'package:commons_core/commons_core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 
@@ -100,7 +99,7 @@ class _DetailView extends StatelessWidget {
               _SectionTitle(t.detail.lots),
               TextButton.icon(
                 key: const Key('detail.addLot'),
-                onPressed: () => _showAddLotSheet(context, cubit),
+                onPressed: () => _showLotSheet(context, cubit),
                 icon: const Icon(Icons.add),
                 label: Text(t.detail.addLot),
               ),
@@ -111,7 +110,9 @@ class _DetailView extends StatelessWidget {
           else
             for (final lot in detail.lots)
               ListTile(
+                key: Key('lot.${lot.id}'),
                 contentPadding: EdgeInsets.zero,
+                onTap: () => _showLotSheet(context, cubit, existing: lot),
                 leading: lot.quantity == null
                     ? const Icon(Icons.inventory_2_outlined)
                     : QuantityKindIcon(lot.quantity!.kind, size: 28),
@@ -475,15 +476,20 @@ class _EditVarietySheetState extends State<_EditVarietySheet> {
   }
 }
 
-Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
+Future<void> _showLotSheet(
+  BuildContext context,
+  VarietyDetailCubit cubit, {
+  VarietyLot? existing,
+}) {
   final t = context.t;
   final currentYear = DateTime.now().year;
   // Harvest years: current year down through the last four decades. Newest
   // first because a freshly harvested lot is the common case.
   final years = [for (var y = currentYear; y >= currentYear - 40; y--) y];
-  var selectedYear = currentYear;
-  var selectedType = LotType.seed;
-  Quantity? selectedQuantity;
+  var selectedYear = existing?.harvestYear ?? currentYear;
+  var selectedType = existing?.type ?? LotType.seed;
+  var selectedQuantity = existing?.quantity;
+  final editing = existing != null;
   return showModalBottomSheet<void>(
     context: context,
     isScrollControlled: true,
@@ -499,9 +505,25 @@ Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
           mainAxisSize: MainAxisSize.min,
           crossAxisAlignment: CrossAxisAlignment.stretch,
           children: [
-            Text(
-              t.addLot.title,
-              style: Theme.of(sheetContext).textTheme.titleLarge,
+            Row(
+              children: [
+                Expanded(
+                  child: Text(
+                    editing ? t.detail.editLot : t.addLot.title,
+                    style: Theme.of(sheetContext).textTheme.titleLarge,
+                  ),
+                ),
+                if (editing)
+                  IconButton(
+                    key: const Key('lot.delete'),
+                    icon: const Icon(Icons.delete_outline),
+                    tooltip: t.common.delete,
+                    onPressed: () {
+                      cubit.deleteLot(existing.id);
+                      Navigator.of(sheetContext).pop();
+                    },
+                  ),
+              ],
             ),
             const SizedBox(height: 12),
             LotTypeSelector(
@@ -549,11 +571,20 @@ Future<void> _showAddLotSheet(BuildContext context, VarietyDetailCubit cubit) {
                 FilledButton(
                   key: const Key('addLot.save'),
                   onPressed: () {
-                    cubit.addLot(
-                      type: selectedType,
-                      year: selectedYear,
-                      quantity: selectedQuantity,
-                    );
+                    if (editing) {
+                      cubit.updateLot(
+                        lotId: existing.id,
+                        type: selectedType,
+                        year: selectedYear,
+                        quantity: selectedQuantity,
+                      );
+                    } else {
+                      cubit.addLot(
+                        type: selectedType,
+                        year: selectedYear,
+                        quantity: selectedQuantity,
+                      );
+                    }
                     Navigator.of(sheetContext).pop();
                   },
                   child: Text(t.common.save),