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/i18n/ast.i18n.json

@@ -37,6 +37,7 @@
     "wishlist": "Llista de deseos",
     "following": "Siguiendo",
     "plantares": "Plantares",
+    "sales": "Ventes",
     "settings": "Axustes"
   },
   "settings": {
@@ -577,5 +578,23 @@
     "openSection": "Pendientes",
     "settledSection": "Fechos",
     "removeConfirm": "¿Quitar esti compromisu?"
+  },
+  "sale": {
+    "title": "Ventes",
+    "help": "Rexistra semilla vendida o mercada — dineru, Ğ1 o cualquier moneda. Un modelu aparte del regalu y del Plantare. Enxamás se cobra comisión poles semilles.",
+    "add": "Rexistrar venta",
+    "empty": "Entá nun hai ventes. Anota equí lo que vendes o merques.",
+    "iSold": "Vendí",
+    "iBought": "Mercué",
+    "direction": "¿Vendes o merques?",
+    "counterparty": "¿Con quién?",
+    "counterpartyHint": "Una persona o un coleutivu (opcional)",
+    "amount": "Importe",
+    "currency": "Moneda",
+    "currencyHint": "€, Ğ1, hores… (opcional)",
+    "note": "Nota (opcional)",
+    "save": "Guardar",
+    "delete": "Quitar",
+    "removeConfirm": "¿Quitar esta venta?"
   }
 }