feat(app): hint isolation distance when sowing a cross-pollinating crop

One passive line in the batch story after a 'sown today' tap — 'this
species crosses, grow it ~400 m from others' — sourced from the bundled
seed-saving guidance (family default + species override). Selfers get
nothing: the trap is recording isolation religiously for beans where it
never mattered. No input fields, no schema change.

apps/app_seeds/lib/ui/lot_history_sheet.dart

@@ -3,6 +3,7 @@ import 'package:intl/intl.dart';
 
 import '../data/variety_repository.dart';
 import '../db/enums.dart';
+import '../domain/seed_saving.dart';
 import '../i18n/strings.g.dart';
 import 'quantity_kind_l10n.dart';
 
@@ -14,20 +15,31 @@ Future<void> showLotHistorySheet(
   BuildContext context, {
   required VarietyRepository repository,
   required VarietyLot lot,
+  SeedSavingGuide? guide,
 }) {
   return showModalBottomSheet<void>(
     context: context,
     isScrollControlled: true,
-    builder: (_) => _LotHistorySheet(repository: repository, lot: lot),
+    builder: (_) =>
+        _LotHistorySheet(repository: repository, lot: lot, guide: guide),
   );
 }
 
 class _LotHistorySheet extends StatefulWidget {
-  const _LotHistorySheet({required this.repository, required this.lot});
+  const _LotHistorySheet({
+    required this.repository,
+    required this.lot,
+    this.guide,
+  });
 
   final VarietyRepository repository;
   final VarietyLot lot;
 
+  /// Bundled species guidance, or null. Only read to drop the one-line
+  /// isolation hint when a cross-pollinating crop is sown — selfers get
+  /// nothing (the fields people record religiously where they don't matter).
+  final SeedSavingGuide? guide;
+
   @override
   State<_LotHistorySheet> createState() => _LotHistorySheetState();
 }
@@ -43,6 +55,10 @@ class _LotHistorySheetState extends State<_LotHistorySheet> {
   bool _askOutcome = false;
   final _outcomeNote = TextEditingController();
 
+  // One passive line after sowing a crosser ("this species crosses — isolate
+  // ~400 m"). Never shown for selfers, never an input.
+  bool _showSowingHint = false;
+
   @override
   void initState() {
     super.initState();
@@ -74,9 +90,14 @@ class _LotHistorySheetState extends State<_LotHistorySheet> {
         ),
       ),
     );
+    final guide = widget.guide;
     setState(() {
       _saving = false;
       _askOutcome = type == MovementType.harvested;
+      _showSowingHint =
+          type == MovementType.sown &&
+          guide?.pollination == Pollination.cross &&
+          guide?.isolationMinM != null;
       _history = widget.repository.lotHistory(widget.lot.id);
     });
   }
@@ -146,6 +167,25 @@ class _LotHistorySheetState extends State<_LotHistorySheet> {
                 ),
               ],
             ),
+            if (_showSowingHint)
+              Padding(
+                key: const Key('history.isolationHint'),
+                padding: const EdgeInsetsDirectional.only(top: 8, start: 4),
+                child: Row(
+                  children: [
+                    const Icon(Icons.lightbulb_outline, size: 16),
+                    const SizedBox(width: 6),
+                    Expanded(
+                      child: Text(
+                        context.t.history.isolationHint(
+                          meters: widget.guide!.isolationMinM!,
+                        ),
+                        style: Theme.of(context).textTheme.bodySmall,
+                      ),
+                    ),
+                  ],
+                ),
+              ),
             if (_askOutcome) ...[
               const SizedBox(height: 8),
               _OutcomeQuestion(