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/i18n/ast.i18n.json

@@ -303,6 +303,8 @@
     "add": "¿Compártesla?",
     "title": "¿Compártesla?",
     "nudge": "Tienes a esgaya: podríes compartir un poco.",
+    "price": "Preciu",
+    "priceHint": "Déxalu baleru p'alcordalu depués",
     "private": "Namás pa min",
     "gift": "Pa regalar",
     "exchange": "Pa trocar",

apps/app_seeds/lib/i18n/en.i18n.json

@@ -304,6 +304,8 @@
     "add": "Do you share it?",
     "title": "Do you share it?",
     "nudge": "You have plenty — you could share some.",
+    "price": "Price",
+    "priceHint": "Leave it empty to agree it later",
     "private": "Just for me",
     "gift": "To give away",
     "exchange": "To swap",

apps/app_seeds/lib/i18n/es.i18n.json

@@ -303,6 +303,8 @@
     "add": "¿La compartes?",
     "title": "¿La compartes?",
     "nudge": "Tienes de sobra: podrías compartir un poco.",
+    "price": "Precio",
+    "priceHint": "Déjalo vacío para acordarlo luego",
     "private": "Solo para mí",
     "gift": "Para regalar",
     "exchange": "Para intercambiar",

apps/app_seeds/lib/i18n/pt.i18n.json

@@ -300,6 +300,8 @@
     "add": "Partilhas esta?",
     "title": "Partilhas esta?",
     "nudge": "Tens de sobra: podias partilhar um pouco.",
+    "price": "Preço",
+    "priceHint": "Deixa vazio para combinar depois",
     "private": "Só para mim",
     "gift": "Para dar",
     "exchange": "Para trocar",

apps/app_seeds/lib/i18n/strings.g.dart

@@ -4,9 +4,9 @@
 /// To regenerate, run: `dart run slang`
 ///
 /// Locales: 4
-/// Strings: 1968 (492 per locale)
+/// Strings: 1976 (494 per locale)
 ///
-/// Built on 2026-07-11 at 05:50 UTC
+/// Built on 2026-07-11 at 06:00 UTC
 
 // coverage:ignore-file
 // ignore_for_file: type=lint, unused_import

apps/app_seeds/lib/i18n/strings_ast.g.dart

@@ -547,6 +547,8 @@ class _Translations$share$ast extends Translations$share$en {
 	@override String get add => '¿Compártesla?';
 	@override String get title => '¿Compártesla?';
 	@override String get nudge => 'Tienes a esgaya: podríes compartir un poco.';
+	@override String get price => 'Preciu';
+	@override String get priceHint => 'Déxalu baleru p\'alcordalu depués';
 	@override String get private => 'Namás pa min';
 	@override String get gift => 'Pa regalar';
 	@override String get exchange => 'Pa trocar';
@@ -1501,6 +1503,8 @@ extension on TranslationsAst {
 			'share.add' => '¿Compártesla?',
 			'share.title' => '¿Compártesla?',
 			'share.nudge' => 'Tienes a esgaya: podríes compartir un poco.',
+			'share.price' => 'Preciu',
+			'share.priceHint' => 'Déxalu baleru p\'alcordalu depués',
 			'share.private' => 'Namás pa min',
 			'share.gift' => 'Pa regalar',
 			'share.exchange' => 'Pa trocar',

apps/app_seeds/lib/i18n/strings_en.g.dart

@@ -988,6 +988,12 @@ class Translations$share$en {
 	/// en: 'You have plenty — you could share some.'
 	String get nudge => 'You have plenty — you could share some.';
 
+	/// en: 'Price'
+	String get price => 'Price';
+
+	/// en: 'Leave it empty to agree it later'
+	String get priceHint => 'Leave it empty to agree it later';
+
 	/// en: 'Just for me'
 	String get private => 'Just for me';
 
@@ -2473,6 +2479,8 @@ extension on Translations {
 			'share.add' => 'Do you share it?',
 			'share.title' => 'Do you share it?',
 			'share.nudge' => 'You have plenty — you could share some.',
+			'share.price' => 'Price',
+			'share.priceHint' => 'Leave it empty to agree it later',
 			'share.private' => 'Just for me',
 			'share.gift' => 'To give away',
 			'share.exchange' => 'To swap',

apps/app_seeds/lib/i18n/strings_es.g.dart

@@ -547,6 +547,8 @@ class _Translations$share$es extends Translations$share$en {
 	@override String get add => '¿La compartes?';
 	@override String get title => '¿La compartes?';
 	@override String get nudge => 'Tienes de sobra: podrías compartir un poco.';
+	@override String get price => 'Precio';
+	@override String get priceHint => 'Déjalo vacío para acordarlo luego';
 	@override String get private => 'Solo para mí';
 	@override String get gift => 'Para regalar';
 	@override String get exchange => 'Para intercambiar';
@@ -1503,6 +1505,8 @@ extension on TranslationsEs {
 			'share.add' => '¿La compartes?',
 			'share.title' => '¿La compartes?',
 			'share.nudge' => 'Tienes de sobra: podrías compartir un poco.',
+			'share.price' => 'Precio',
+			'share.priceHint' => 'Déjalo vacío para acordarlo luego',
 			'share.private' => 'Solo para mí',
 			'share.gift' => 'Para regalar',
 			'share.exchange' => 'Para intercambiar',

apps/app_seeds/lib/i18n/strings_pt.g.dart

@@ -544,6 +544,8 @@ class _Translations$share$pt extends Translations$share$en {
 	@override String get add => 'Partilhas esta?';
 	@override String get title => 'Partilhas esta?';
 	@override String get nudge => 'Tens de sobra: podias partilhar um pouco.';
+	@override String get price => 'Preço';
+	@override String get priceHint => 'Deixa vazio para combinar depois';
 	@override String get private => 'Só para mim';
 	@override String get gift => 'Para dar';
 	@override String get exchange => 'Para trocar';
@@ -1497,6 +1499,8 @@ extension on TranslationsPt {
 			'share.add' => 'Partilhas esta?',
 			'share.title' => 'Partilhas esta?',
 			'share.nudge' => 'Tens de sobra: podias partilhar um pouco.',
+			'share.price' => 'Preço',
+			'share.priceHint' => 'Deixa vazio para combinar depois',
 			'share.private' => 'Só para mim',
 			'share.gift' => 'Para dar',
 			'share.exchange' => 'Para trocar',