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/variety_detail_screen.dart

@@ -237,6 +237,10 @@ class _DetailView extends StatelessWidget {
                 cubit: cubit,
                 lot: lot,
                 viabilityYears: detail.viabilityYears,
+                guide: SeedSavingCatalog.guideFor(
+                  scientificName: detail.scientificName,
+                  family: detail.family ?? detail.category,
+                ),
               ),
           _PlantaresSection(varietyId: detail.id),
         ],
@@ -375,6 +379,7 @@ class _LotTile extends StatelessWidget {
     required this.cubit,
     required this.lot,
     required this.viabilityYears,
+    this.guide,
   });
 
   final VarietyDetailCubit cubit;
@@ -383,6 +388,10 @@ class _LotTile extends StatelessWidget {
   /// Typical seed longevity of the variety's species (years), or null.
   final int? viabilityYears;
 
+  /// Bundled seed-saving guidance for the species, or null — lets the history
+  /// sheet drop a one-line isolation hint when a crosser is sown.
+  final SeedSavingGuide? guide;
+
   @override
   Widget build(BuildContext context) {
     final t = context.t;
@@ -443,6 +452,7 @@ class _LotTile extends StatelessWidget {
               context,
               repository: context.read<VarietyRepository>(),
               lot: lot,
+              guide: guide,
             ),
           ),
           IconButton(