feat(offers): asking price on lots, published with sale offers (schema v11)

The data model always meant sale offers to carry an informational price
(data-model §2.8, sharing-model §4.4); with offer state collapsed onto
the Lot, the price lives there. Null amount on a sell lot = 'to be
agreed' — the NIP-99 event simply omits the price tag.

- schema v11: Lots.price_amount/price_currency, guarded migration,
  schema dump + generated schema_v11 for the round-trip test
- ShareableLot/VarietyLot carry the price (sell-only in shareableLots);
  addLot/updateLot persist it and clear it when the lot leaves sale
- OffersCubit.publishLots forwards it (outbox flush picks it up free)
- lot sheet: price + currency inputs revealed only on 'For sale', with
  the €/Ğ1/hours quick-picks extracted to a shared CurrencyQuickPicks
  widget (reused by the sale sheet)
- backup JSON round-trips the new columns
- i18n share.price/priceHint in en/es/pt/ast

apps/app_seeds/test/state/offers_cubit_test.dart

@@ -294,6 +294,43 @@ void main() {
       await cubit.close();
     });
 
+    test('publishLots carries the lot asking price on sale offers', () async {
+      final transport = FakeOfferTransport();
+      final cubit = OffersCubit(transport);
+      await cubit.publishLots(
+        const [
+          ShareableLot(
+            lotId: 'lot-sale',
+            varietyId: 'var-1',
+            summary: 'Tomate',
+            offerStatus: OfferStatus.sell,
+            priceAmount: 3.5,
+            priceCurrency: 'Ğ1',
+          ),
+          // "To be agreed": sale without a figure publishes without a price.
+          ShareableLot(
+            lotId: 'lot-negotiable',
+            varietyId: 'var-2',
+            summary: 'Judía',
+            offerStatus: OfferStatus.sell,
+          ),
+        ],
+        authorPubkeyHex: 'ab' * 32,
+        areaGeohash: 'sp3e9',
+      );
+
+      await cubit.discover('sp3');
+      await pumpEventQueue();
+      final sale = cubit.state.offers.singleWhere((o) => o.id == 'lot-sale');
+      expect(sale.type, OfferType.sale);
+      expect(sale.priceAmount, 3.5);
+      expect(sale.priceCurrency, 'Ğ1');
+      final negotiable =
+          cubit.state.offers.singleWhere((o) => o.id == 'lot-negotiable');
+      expect(negotiable.priceAmount, isNull);
+      await cubit.close();
+    });
+
     test('publishLots embeds an inline thumbnail data-URI on the offer',
         () async {
       final transport = FakeOfferTransport();