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/i18n/strings_pt.g.dart

@@ -615,6 +615,9 @@ class _Translations$market$pt extends Translations$market$en {
 	@override String get save => 'Guardar';
 	@override String get saved => 'Guardado';
 	@override String get wanted => 'Procuro';
+	@override String get shareMine => 'Partilhar as minhas sementes';
+	@override String sharedCount({required Object n}) => 'Partilhadas ${n} sementes';
+	@override String get nothingToShare => 'Marca primeiro algumas sementes para dar, trocar ou vender';
 }
 
 // Path: intro.slides
@@ -1265,6 +1268,9 @@ extension on TranslationsPt {
 			'market.save' => 'Guardar',
 			'market.saved' => 'Guardado',
 			'market.wanted' => 'Procuro',
+			'market.shareMine' => 'Partilhar as minhas sementes',
+			'market.sharedCount' => ({required Object n}) => 'Partilhadas ${n} sementes',
+			'market.nothingToShare' => 'Marca primeiro algumas sementes para dar, trocar ou vender',
 			_ => null,
 		};
 	}