feat(plantare): surface product link + dates; spec the bilateral record

The Plantaré screen stored madeOn/dueBy/varietyId but showed none of them,
so it felt half-built. Surface what's already there (no schema change):

- watchPlantareViews() joins each commitment with its variety label
- tile shows the made-on date, a "Return by {date}" line (amber + "overdue"
  when an open promise is past due, via new seedWarning colour), the variety
  name, and taps through to /variety/:id
- add sheet gains an optional return-by date picker (createPlantare already
  took dueBy)
- variety detail shows a read-only commitments section (hidden when empty,
  no add button — honours the single hand-over door)
- i18n en/es/pt/ast; tests for the join, dueBy round-trip, tile, and section

Also specs the deferred two-sided record in docs/design/plantare-bilateral.md
(Nostr pubkey counterparty, PlantareTransport propose->accept->counter-sign,
deferred key/signature/movement columns, provenance DAG, reputation anchor),
with a faithful transcription of the paper Plantaré v0.4 (BAH-Semillero 2009,
CC-BY-SA). Cross-linked from data-model §2.7 and sharing-model §6.

apps/app_seeds/lib/ui/variety_detail_screen.dart

@@ -9,6 +9,7 @@ import 'package:url_launcher/url_launcher.dart';
 import '../data/seed_saving_catalog.dart';
 import '../data/species_repository.dart';
 import '../data/variety_repository.dart';
+import '../db/database.dart';
 import '../db/enums.dart';
 import '../domain/crop_calendar.dart';
 import '../domain/seed_saving.dart';
@@ -235,6 +236,106 @@ class _DetailView extends StatelessWidget {
                 lot: lot,
                 viabilityYears: detail.viabilityYears,
               ),
+          _PlantaresSection(varietyId: detail.id),
+        ],
+      ),
+    );
+  }
+}
+
+/// The reproduction commitments (Plantarés) recorded against this variety — so
+/// a promise to grow it out and pass it on lives next to the seed it's about,
+/// not only on the separate Plantares screen. Read-only: new ones are recorded
+/// through the single hand-over door (or the Plantares screen), and the section
+/// stays hidden until there's something to show, like the other detail blocks.
+class _PlantaresSection extends StatelessWidget {
+  const _PlantaresSection({required this.varietyId});
+
+  final String varietyId;
+
+  @override
+  Widget build(BuildContext context) {
+    final t = context.t;
+    final repo = context.read<VarietyRepository>();
+    return StreamBuilder<List<Plantare>>(
+      stream: repo.watchPlantaresForVariety(varietyId),
+      builder: (context, snapshot) {
+        final list = snapshot.data ?? const <Plantare>[];
+        if (list.isEmpty) return const SizedBox.shrink();
+        return Column(
+          key: const Key('detail.plantares'),
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            const SizedBox(height: 16),
+            _SectionTitle(t.plantare.sectionTitle),
+            for (final p in list) _PlantareLine(p),
+          ],
+        );
+      },
+    );
+  }
+}
+
+/// A compact, read-only commitment row for the variety detail: direction,
+/// counterparty and when — with a return-by line (amber when overdue).
+class _PlantareLine extends StatelessWidget {
+  const _PlantareLine(this.p);
+
+  final Plantare p;
+
+  @override
+  Widget build(BuildContext context) {
+    final t = context.t;
+    final locals = MaterialLocalizations.of(context);
+    final done = p.status != PlantareStatus.open;
+    final iReturn = p.direction == PlantareDirection.iReturn;
+    final title = (p.owedDescription?.trim().isNotEmpty ?? false)
+        ? p.owedDescription!.trim()
+        : (iReturn ? t.plantare.iReturn : t.plantare.owedToMe);
+    final parts = <String>[
+      iReturn ? t.plantare.iReturn : t.plantare.owedToMe,
+      if (p.counterparty?.trim().isNotEmpty ?? false) p.counterparty!.trim(),
+      locals.formatShortDate(DateTime.fromMillisecondsSinceEpoch(p.madeOn)),
+      if (done)
+        p.status == PlantareStatus.returned
+            ? t.plantare.statusReturned
+            : t.plantare.statusForgiven,
+    ];
+    final overdue = !done &&
+        p.dueBy != null &&
+        p.dueBy! < DateTime.now().millisecondsSinceEpoch;
+    final returnBy = p.dueBy == null
+        ? null
+        : t.plantare.returnBy(
+            date: locals.formatShortDate(
+              DateTime.fromMillisecondsSinceEpoch(p.dueBy!),
+            ),
+          );
+    return ListTile(
+      contentPadding: EdgeInsets.zero,
+      leading: Icon(
+        iReturn ? Icons.volunteer_activism_outlined : Icons.eco_outlined,
+        color: done ? seedMuted : seedGreen,
+      ),
+      title: Text(
+        title,
+        style: TextStyle(
+          decoration: done ? TextDecoration.lineThrough : null,
+          color: done ? seedMuted : seedOnSurface,
+        ),
+      ),
+      subtitle: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          Text(parts.join(' · '), maxLines: 2, overflow: TextOverflow.ellipsis),
+          if (returnBy != null)
+            Text(
+              overdue ? '$returnBy · ${t.plantare.overdue}' : returnBy,
+              style: TextStyle(
+                color: overdue ? seedWarning : seedMuted,
+                fontWeight: overdue ? FontWeight.w600 : null,
+              ),
+            ),
         ],
       ),
     );