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/test/ui/small_screen_overflow_test.dart

@@ -17,6 +17,7 @@ import 'package:tane/ui/inventory_list_screen.dart';
 import 'package:tane/ui/market_screen.dart';
 import 'package:tane/ui/plantares_screen.dart';
 import 'package:tane/ui/profile_screen.dart';
+import 'package:tane/ui/sales_screen.dart';
 import 'package:tane/ui/settings_screen.dart';
 
 import '../support/test_support.dart';
@@ -51,6 +52,19 @@ void main() {
     tester.view.devicePixelRatio = 1.0;
     addTearDown(tester.view.resetPhysicalSize);
     addTearDown(tester.view.resetDevicePixelRatio);
+    // flutter_test's headless engine can't decode our real PNG assets (the
+    // logo), so `Image.asset` throws from the "image resource service". That's
+    // unrelated to layout — swallow ONLY those, and let every other FlutterError
+    // (crucially the "rendering library" RenderFlex overflow this guard exists
+    // to catch) still fail the test. Installed here, inside the running test,
+    // because testWidgets reinstalls its own onError at test start (a setUp
+    // override would be clobbered).
+    final previous = FlutterError.onError;
+    FlutterError.onError = (details) {
+      if (details.library == 'image resource service') return;
+      previous?.call(details);
+    };
+    addTearDown(() => FlutterError.onError = previous);
     await tester.pumpWidget(widget);
     await tester.pumpAndSettle();
   }
@@ -258,6 +272,28 @@ void main() {
     await disposeTree(tester);
   });
 
+  testWidgets('the Sales screen (with a sale) fits a small screen',
+      (tester) async {
+    final db = newTestDatabase();
+    addTearDown(db.close);
+    final repo = newTestRepository(db);
+    await repo.createSale(
+      direction: SaleDirection.iSold,
+      counterparty: 'Feria de intercambio de la comarca',
+      amount: 12.5,
+      currency: '€',
+    );
+    await pumpSmall(
+      tester,
+      wrapScreen(
+        repository: repo,
+        locale: AppLocale.es,
+        child: const SalesScreen(),
+      ),
+    );
+    await disposeTree(tester);
+  });
+
   // NOTE: the variety-detail screen is deliberately NOT overflow-checked here.
   // It reports a ~2px overflow on a RenderFlex that is already DISPOSED/DEFUNCT
   // — a transient stale frame while its cubit's Drift stream rebuilds during