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/test/state/offers_cubit_test.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:commons_core/commons_core.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/data/variety_repository.dart';
 import 'package:tane/db/enums.dart';
 import 'package:tane/services/offer_mapper.dart';
 import 'package:tane/state/offers_cubit.dart';
@@ -129,6 +130,72 @@ void main() {
       await cubit.close();
     });
 
+    test('publishLots publishes each shared lot and counts acceptances',
+        () async {
+      final transport = FakeOfferTransport();
+      final cubit = OffersCubit(transport);
+      final count = await cubit.publishLots(
+        const [
+          ShareableLot(
+            lotId: 'lot-1',
+            summary: 'Tomate',
+            offerStatus: OfferStatus.shared,
+            category: 'Solanaceae',
+          ),
+          ShareableLot(
+            lotId: 'lot-2',
+            summary: 'Judía',
+            offerStatus: OfferStatus.exchange,
+          ),
+        ],
+        authorPubkeyHex: 'ab' * 32,
+        areaGeohash: 'sp3e9',
+      );
+      expect(count, 2);
+      expect(cubit.state.publishing, isFalse);
+
+      await cubit.discover('sp3');
+      await pumpEventQueue();
+      expect(cubit.state.offers, hasLength(2));
+      await cubit.close();
+    });
+
+    test('publishLots is a no-op offline or with no area', () async {
+      final offline = OffersCubit(null);
+      expect(
+        await offline.publishLots(
+          const [
+            ShareableLot(
+              lotId: 'x',
+              summary: 'x',
+              offerStatus: OfferStatus.shared,
+            ),
+          ],
+          authorPubkeyHex: 'ab' * 32,
+          areaGeohash: 'sp3e9',
+        ),
+        0,
+      );
+      await offline.close();
+
+      final noArea = OffersCubit(FakeOfferTransport());
+      expect(
+        await noArea.publishLots(
+          const [
+            ShareableLot(
+              lotId: 'x',
+              summary: 'x',
+              offerStatus: OfferStatus.shared,
+            ),
+          ],
+          authorPubkeyHex: 'ab' * 32,
+          areaGeohash: '',
+        ),
+        0,
+      );
+      await noArea.close();
+    });
+
     test('offline (no transport): degrades gracefully, never throws', () async {
       final cubit = OffersCubit(null);
       expect(cubit.isOnline, isFalse);