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/ui/sales_screen.dart

@@ -0,0 +1,111 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
+
+import '../data/variety_repository.dart';
+import '../db/database.dart';
+import '../db/enums.dart';
+import '../i18n/strings.g.dart';
+import 'sale_sheet.dart';
+import 'theme.dart';
+
+/// The Sales screen — a local ledger of seed sold or bought, in any currency.
+/// A model separate from a gift or a Plantare. Reads the encrypted inventory DB.
+class SalesScreen extends StatelessWidget {
+  const SalesScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final t = context.t;
+    final repo = context.read<VarietyRepository>();
+    return Scaffold(
+      appBar: AppBar(title: Text(t.sale.title)),
+      floatingActionButton: FloatingActionButton.extended(
+        key: const Key('sales.add'),
+        onPressed: () => showSaleSheet(context, repository: repo),
+        icon: const Icon(Icons.add),
+        label: Text(t.sale.add),
+      ),
+      body: StreamBuilder<List<Sale>>(
+        stream: repo.watchSales(),
+        builder: (context, snapshot) {
+          final sales = snapshot.data;
+          if (sales == null) {
+            return const Center(child: CircularProgressIndicator());
+          }
+          if (sales.isEmpty) {
+            return Center(
+              child: Padding(
+                padding: const EdgeInsets.all(32),
+                child: Text(
+                  t.sale.empty,
+                  textAlign: TextAlign.center,
+                  style: const TextStyle(color: seedMuted, fontSize: 15),
+                ),
+              ),
+            );
+          }
+          return ListView.separated(
+            padding: const EdgeInsets.only(bottom: 88),
+            itemCount: sales.length,
+            separatorBuilder: (_, _) => const Divider(height: 1),
+            itemBuilder: (context, i) => _SaleTile(sales[i], repo),
+          );
+        },
+      ),
+    );
+  }
+}
+
+class _SaleTile extends StatelessWidget {
+  const _SaleTile(this.s, this.repo);
+
+  final Sale s;
+  final VarietyRepository repo;
+
+  String _money() {
+    final amount = s.amount;
+    if (amount == null) return s.currency?.trim() ?? '';
+    // Drop a trailing .0 so "5.0 €" reads "5 €".
+    final n = amount == amount.roundToDouble()
+        ? amount.toInt().toString()
+        : amount.toString();
+    return [n, s.currency?.trim()].where((e) => e != null && e.isNotEmpty).join(' ');
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final t = context.t;
+    final iSold = s.direction == SaleDirection.iSold;
+    final money = _money();
+    final date = MaterialLocalizations.of(context)
+        .formatShortDate(DateTime.fromMillisecondsSinceEpoch(s.soldOn));
+    final subtitle = [
+      iSold ? t.sale.iSold : t.sale.iBought,
+      if (s.counterparty?.trim().isNotEmpty ?? false) s.counterparty!.trim(),
+      date,
+    ].join(' · ');
+    return ListTile(
+      leading: Icon(
+        iSold ? Icons.sell_outlined : Icons.shopping_bag_outlined,
+        color: seedGreen,
+      ),
+      title: Text(
+        money.isEmpty
+            ? (s.note?.trim().isNotEmpty ?? false
+                ? s.note!.trim()
+                : (iSold ? t.sale.iSold : t.sale.iBought))
+            : money,
+        style: const TextStyle(fontWeight: FontWeight.w600),
+      ),
+      subtitle: Text(subtitle, maxLines: 2, overflow: TextOverflow.ellipsis),
+      trailing: PopupMenuButton<String>(
+        key: Key('sale.menu.${s.id}'),
+        onSelected: (v) {
+          if (v == 'delete') repo.deleteSale(s.id);
+        },
+        itemBuilder: (context) =>
+            [PopupMenuItem(value: 'delete', child: Text(t.sale.delete))],
+      ),
+    );
+  }
+}