feat(block2): publish my seeds to the network (completes publish->discover)

The other half of the market: share your marked lots as offers.
- VarietyRepository.shareableLots(): non-private lots WITH their id (stable,
  updatable offer id) + the variety label. Private lots never leave the device.
- OffersCubit.publishLots(): maps each via OfferMapper and publishes, tagged
  with the coarse area + signed by the derived key; counts acceptances; no-op
  offline or with no area.
- Market screen: a 'share my seeds' action (online only) — publishes, then
  re-discovers to show them; 'mark some seeds first' when nothing's shared.
- i18n en/es/pt.

14 tests green (repo query, cubit publish, market UI); analyzer clean for new code.

apps/app_seeds/lib/data/variety_repository.dart

@@ -117,6 +117,33 @@ class SharedCatalogEntry extends Equatable {
   ];
 }
 
+/// A lot the user has marked for sharing, carrying the lot [lotId] (so the
+/// published offer has a stable, updatable id) plus the summary a network offer
+/// needs. Distinct from [SharedCatalogEntry], which is for the printable local
+/// catalog and has no id.
+class ShareableLot extends Equatable {
+  const ShareableLot({
+    required this.lotId,
+    required this.summary,
+    required this.offerStatus,
+    this.category,
+    this.harvestYear,
+  });
+
+  final String lotId;
+
+  /// What to publish: the variety label (never the full inventory).
+  final String summary;
+
+  /// Never [OfferStatus.private] — private lots don't leave the device.
+  final OfferStatus offerStatus;
+  final String? category;
+  final int? harvestYear;
+
+  @override
+  List<Object?> get props => [lotId, summary, offerStatus, category, harvestYear];
+}
+
 /// One germination test on a lot; [rate] is derived (0..1), null when it can't
 /// be computed.
 class GerminationEntry extends Equatable {
@@ -1210,6 +1237,42 @@ class VarietyRepository {
     return entries;
   }
 
+  /// Lots the user marked to share (not private), each with its id and the
+  /// variety label — the input for publishing offers to the network (Block 2).
+  Future<List<ShareableLot>> shareableLots() async {
+    final lots =
+        await (_db.select(_db.lots)..where(
+              (l) =>
+                  l.isDeleted.equals(false) &
+                  l.offerStatus.equalsValue(OfferStatus.private).not(),
+            ))
+            .get();
+    if (lots.isEmpty) return const [];
+
+    final varietyIds = lots.map((l) => l.varietyId).toSet();
+    final varieties =
+        await (_db.select(_db.varieties)..where(
+              (v) =>
+                  v.id.isIn(varietyIds) &
+                  v.isDeleted.equals(false) &
+                  v.isDraft.equals(false),
+            ))
+            .get();
+    final byId = {for (final v in varieties) v.id: v};
+
+    return [
+      for (final l in lots)
+        if (byId[l.varietyId] case final v?)
+          ShareableLot(
+            lotId: l.id,
+            summary: v.label,
+            offerStatus: l.offerStatus,
+            category: v.category,
+            harvestYear: l.harvestYear,
+          ),
+    ];
+  }
+
   /// Soft-deletes a lot (tombstone); it leaves the variety's lot list.
   Future<void> softDeleteLot(String lotId) async {
     final (_, updated) = await _stamp();