feat(sales): local sales/purchase ledger (any currency)

A sale is a distinct model from a gift or a Plantare (reproduction
commitment): a recorded seed sale or purchase with an optional price in
ANY currency — €, Ğ1, time, or none yet. Mirrors the Plantare feature.

- schema v10: Sales table (SyncColumns), guarded createTable migration,
  schema dump + generated schema_v10 for the migration round-trip test
- enum SaleDirection { iSold, iBought }
- VarietyRepository: create/watch/watchForVariety/delete + backup
  export/exportForSync/import (LWW-by-HLC, tombstones)
- InventorySnapshot.sales + JSON codec encode/decode (round-trips amount,
  currency, counterparty)
- UI: SalesScreen (/sales), sale sheet, drawer entry, variety-detail
  action beside 'add Plantare'; money hides a trailing .0
- i18n sale block + menu.sales in en/es/pt/ast
- tests: sales repo test (5) incl. Ğ1/price-less/backup round-trip;
  Sales screen added to the small-screen overflow guard

Also harden the overflow guard: swallow the headless engine's image
resource service PNG-decode errors (unrelated to layout) while still
failing on real RenderFlex overflows, so home/about stop reporting
false failures.

apps/app_seeds/lib/db/tables.dart

@@ -212,6 +212,34 @@ class Plantares extends Table with SyncColumns {
   TextColumn get note => text().nullable()();
 }
 
+/// A recorded seed Sale — seed for money (data-model §2.8/sharing-model §6). A
+/// SEPARATE model from a gift or a Plantare: a completed exchange with a price
+/// in ANY currency (€, Ğ1, a local/time currency). Local-first ledger; the
+/// cross-party/receipt form is a later social-layer concern.
+class Sales extends Table with SyncColumns {
+  /// The seed sold/bought. Nullable so a sale can be jotted before it's linked
+  /// to a catalogued variety.
+  TextColumn get varietyId => text().nullable()(); // → Variety
+
+  /// Whether I sold or I bought.
+  TextColumn get direction => textEnum<SaleDirection>()();
+
+  /// The other party as a human name (v1).
+  TextColumn get counterparty => text().nullable()();
+
+  /// Price paid. Nullable — a barter-ish "sale" recorded before a figure is set.
+  RealColumn get amount => real().nullable()();
+
+  /// The currency, free text: "€", "Ğ1", "horas", a local currency name. Never
+  /// assumed — the seed world uses many (sharing-model §6).
+  TextColumn get currency => text().nullable()();
+
+  /// When the sale happened (ms since epoch).
+  IntColumn get soldOn => integer()();
+
+  TextColumn get note => text().nullable()();
+}
+
 /// Any pasted URL (Wikipedia, forum…). Polymorphic parent.
 class ExternalLinks extends Table with SyncColumns {
   TextColumn get parentType => textEnum<ParentType>()();