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/data/export_import/inventory_json_codec.dart

@@ -230,6 +230,26 @@ class InventoryJsonCodec {
             'note': p.note,
           },
       ],
+      'sales': [
+        for (final s in snapshot.sales)
+          {
+            ..._syncMeta(
+              id: s.id,
+              createdAt: s.createdAt,
+              updatedAt: s.updatedAt,
+              lastAuthor: s.lastAuthor,
+              schemaRowVersion: s.schemaRowVersion,
+              isDeleted: s.isDeleted,
+            ),
+            'varietyId': s.varietyId,
+            'direction': s.direction.name,
+            'counterparty': s.counterparty,
+            'amount': s.amount,
+            'currency': s.currency,
+            'soldOn': s.soldOn,
+            'note': s.note,
+          },
+      ],
     });
   }
 
@@ -462,6 +482,24 @@ class InventoryJsonCodec {
           note: m['note'] as String?,
         );
       }),
+      sales: _rows(root, 'sales', (m) {
+        return Sale(
+          id: _string(m, 'id'),
+          createdAt: _int(m, 'createdAt'),
+          updatedAt: _string(m, 'updatedAt'),
+          lastAuthor: _string(m, 'lastAuthor'),
+          isDeleted: _bool(m, 'isDeleted'),
+          schemaRowVersion: _int(m, 'schemaRowVersion', fallback: 1),
+          varietyId: m['varietyId'] as String?,
+          direction:
+              _enumOr(SaleDirection.values, m['direction'], SaleDirection.iSold),
+          counterparty: m['counterparty'] as String?,
+          amount: (m['amount'] as num?)?.toDouble(),
+          currency: m['currency'] as String?,
+          soldOn: _int(m, 'soldOn'),
+          note: m['note'] as String?,
+        );
+      }),
     );
   }
 

apps/app_seeds/lib/data/export_import/inventory_snapshot.dart

@@ -31,6 +31,7 @@ class InventorySnapshot {
     this.parties = const [],
     this.attachments = const [],
     this.plantares = const [],
+    this.sales = const [],
     this.speciesNamesById = const {},
   });
 
@@ -44,6 +45,7 @@ class InventorySnapshot {
   final List<Party> parties;
   final List<Attachment> attachments;
   final List<Plantare> plantares;
+  final List<Sale> sales;
 
   /// speciesId → scientificName, for the species referenced by [varieties].
   final Map<String, String> speciesNamesById;