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/lib/db/tables.dart

@@ -109,6 +109,17 @@ class Lots extends Table with SyncColumns {
   /// Distinct from [storageLocation]. Optional.
   TextColumn get preservationFormat =>
       textEnum<PreservationFormat>().nullable()();
+
+  /// Asking price when [offerStatus] is `sell` (data-model §2.8 puts price on
+  /// the Offer; with offer state collapsed onto the Lot, it lives here and is
+  /// published with the market offer). Informational only — money changes
+  /// hands off-platform, never in-app. Null amount on a sell lot means
+  /// "price to be agreed" (the offer publishes without a price).
+  RealColumn get priceAmount => real().nullable()();
+
+  /// Free-text currency, like [Sales.currency]: "€", "Ğ1", a local/time
+  /// currency. Never assumed (sharing-model §6).
+  TextColumn get priceCurrency => text().nullable()();
 }
 
 /// Optional germination history for a Lot; percent is derived in code.