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/ui/currency_quick_picks.dart

@@ -0,0 +1,44 @@
+import 'package:flutter/material.dart';
+
+import '../i18n/strings.g.dart';
+
+/// One-tap currency chips bound to a free-text [controller]. Ğ1 sits quietly
+/// among the familiar ones — offered, never imposed — and free text still
+/// takes anything else (sharing-model §6). Shared by the sale sheet, the lot
+/// price field and the hand-over sheet so every money-ish input feels the same.
+class CurrencyQuickPicks extends StatelessWidget {
+  const CurrencyQuickPicks({
+    required this.controller,
+    required this.keyPrefix,
+    required this.onChanged,
+    super.key,
+  });
+
+  final TextEditingController controller;
+
+  /// Namespaces the chip [Key]s (e.g. `sale` → `sale.currencyChip.€`).
+  final String keyPrefix;
+
+  /// Fires after a chip toggles the controller text (for `setState`).
+  final VoidCallback onChanged;
+
+  @override
+  Widget build(BuildContext context) {
+    final t = context.t;
+    return Wrap(
+      spacing: 8,
+      children: [
+        for (final c in ['€', 'Ğ1', t.sale.hours])
+          ChoiceChip(
+            key: Key('$keyPrefix.currencyChip.$c'),
+            label: Text(c),
+            selected: controller.text.trim() == c,
+            onSelected: (sel) {
+              controller.text = sel ? c : '';
+              onChanged();
+            },
+          ),
+      ],
+    );
+  }
+}