feat(inventory): CSV/JSON export and JSON import with LWW reconciliation

Interchange export/import for Phase 1 (data-model §7):

- JSON: canonical, versioned envelope (formatVersion 1) with all sync
  metadata verbatim, photos embedded as base64, tombstones excluded.
  Species are re-resolved on import by scientific name (catalog ids are
  per-install). Reader tolerates unknown fields/enum values (§5.2) and
  rejects newer format versions with a clear error.
- CSV: export-only spreadsheet flatten, one row per lot, RFC 4180
  escaping, never any photo bytes.
- Import merges by UUIDv7 id in one transaction: insert-if-unknown
  preserving original stamps, last-writer-wins by packed HLC for known
  mutable rows, append-only movements; afterwards the local clock
  receiveEvent()s the newest imported stamp so it never runs behind.
- Settings gains a Backup section (export CSV/JSON, import JSON with
  confirmation); file dialogs behind a FileService interface backed by
  file_picker (MIT).
- Tests: codec round-trip and tolerance, reconciler LWW, repository
  export→import round-trip (fresh DB, idempotent re-import, newer-local
  wins, clock monotonicity, species re-resolution), backup widget flows.

apps/app_seeds/lib/i18n/es.i18n.json

@@ -43,6 +43,23 @@
     "aboutText": "Inventario local y cifrado para semillas tradicionales. AGPL-3.0.",
     "aboutOpen": "Acerca de Tanemaki"
   },
+  "backup": {
+    "title": "Copia de seguridad",
+    "exportCsv": "Exportar a CSV",
+    "exportCsvSubtitle": "Para hojas de cálculo — sin fotos",
+    "exportJson": "Exportar a JSON",
+    "exportJsonSubtitle": "Copia completa, se puede volver a importar",
+    "importJson": "Importar desde JSON",
+    "importJsonSubtitle": "Fusiona una copia guardada con este inventario",
+    "importConfirmTitle": "¿Importar una copia guardada?",
+    "importConfirmBody": "Las entradas se fusionan con tu inventario; si una entrada existe en ambos lados, gana la versión más reciente. No se duplica nada.",
+    "importAction": "Importar",
+    "exportSaved": "Copia guardada",
+    "cancelled": "Cancelado",
+    "importDone": "Importado: {added} nuevas, {updated} actualizadas",
+    "importFailed": "Este fichero no se pudo leer como una copia de Tanemaki",
+    "failed": "Algo ha salido mal"
+  },
   "about": {
     "title": "Acerca de",
     "kanji": "種まき",