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/data/shareable_lots_test.dart

@@ -40,4 +40,71 @@ void main() {
     final lots = await repo.shareableLots();
     expect(lots.where((l) => l.lotId == privateId), isEmpty);
   });
+
+  test('sell lots expose their asking price; other statuses never do',
+      () async {
+    final repo = newTestRepository(db);
+    final varietyId = await repo.addQuickVariety(label: 'Calabaza');
+    final sellId = await repo.addLot(
+      varietyId: varietyId,
+      offerStatus: OfferStatus.sell,
+      priceAmount: 3.5,
+      priceCurrency: 'Ğ1',
+    );
+    // Price passed on a gift lot is dropped, not stored.
+    final giftId = await repo.addLot(
+      varietyId: varietyId,
+      offerStatus: OfferStatus.shared,
+      priceAmount: 99,
+      priceCurrency: '€',
+    );
+
+    final lots = await repo.shareableLots();
+    final sell = lots.singleWhere((l) => l.lotId == sellId);
+    expect(sell.priceAmount, 3.5);
+    expect(sell.priceCurrency, 'Ğ1');
+    final gift = lots.singleWhere((l) => l.lotId == giftId);
+    expect(gift.priceAmount, isNull);
+    expect(gift.priceCurrency, isNull);
+  });
+
+  test('a sell lot without amount is "to be agreed" — shareable, no price',
+      () async {
+    final repo = newTestRepository(db);
+    final varietyId = await repo.addQuickVariety(label: 'Lechuga');
+    final sellId = await repo.addLot(
+      varietyId: varietyId,
+      offerStatus: OfferStatus.sell,
+    );
+
+    final lots = await repo.shareableLots();
+    final sell = lots.singleWhere((l) => l.lotId == sellId);
+    expect(sell.priceAmount, isNull);
+  });
+
+  test('moving a lot out of sale clears its stored price', () async {
+    final repo = newTestRepository(db);
+    final varietyId = await repo.addQuickVariety(label: 'Haba');
+    final lotId = await repo.addLot(
+      varietyId: varietyId,
+      offerStatus: OfferStatus.sell,
+      priceAmount: 2,
+      priceCurrency: '€',
+    );
+
+    await repo.updateLot(
+      lotId: lotId,
+      type: LotType.seed,
+      offerStatus: OfferStatus.shared,
+      // Price args still sent by the form; must be ignored off-sale.
+      priceAmount: 2,
+      priceCurrency: '€',
+    );
+
+    final detail = await repo.watchVariety(varietyId).first;
+    final lot = detail!.lots.singleWhere((l) => l.id == lotId);
+    expect(lot.priceAmount, isNull);
+    expect(lot.priceCurrency, isNull);
+    expect(lot.offerStatus, OfferStatus.shared);
+  });
 }