feat(app): show each batch's story as a composite timeline

The Movement log (history + provenance DAG) was recorded but invisible.
A new history sheet on every lot tile narrates the batch: movements,
germination tests, storage checks and how it entered the collection
(origin attached), most-recent first. Two one-tap chips record 'sown
today' / 'harvested today' — the first UI door to the sown/harvested
movement types. No schema change; one-shot reads only (no live
subscriptions in a transient sheet).

apps/app_seeds/lib/ui/variety_detail_screen.dart

@@ -19,6 +19,7 @@ import '../i18n/strings.g.dart';
 import '../state/variety_detail_cubit.dart';
 import 'currency_quick_picks.dart';
 import 'handover_sheet.dart';
+import 'lot_history_sheet.dart';
 import 'harvest_date_picker.dart';
 import 'photo_pick.dart';
 import 'quantity_kind_l10n.dart';
@@ -434,6 +435,16 @@ class _LotTile extends StatelessWidget {
         children: [
           if (lot.type == LotType.seed && lot.latestGerminationRate != null)
             _GerminationBadge(rate: lot.latestGerminationRate!),
+          IconButton(
+            key: Key('lot.history.${lot.id}'),
+            icon: const Icon(Icons.history),
+            tooltip: t.history.tooltip,
+            onPressed: () => showLotHistorySheet(
+              context,
+              repository: context.read<VarietyRepository>(),
+              lot: lot,
+            ),
+          ),
           IconButton(
             key: Key('lot.handover.${lot.id}'),
             icon: const Icon(Icons.handshake_outlined),