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.
