Import a spreadsheet list (the same 21-column schema the CSV export
already produces) as new varieties/lots. Tolerant reader: columns
matched by header name in any order, only variety_label required,
unknown enums fall back to a safe default, rows sharing variety_id
collapse into one variety with several lots. Species re-linked by
scientific name. Additive by design (fresh ids + HLC), so it never
overwrites existing rows; JSON stays the canonical id-reconciling import.
Adds a hand-rolled RFC 4180 parser (no new dependency), an importCsv
path in VarietyRepository/ExportImportService, an 'Import from CSV'
tile in the backup section, and en/es strings.
Note: i18n .g.dart also carries pre-existing About/intro strings from
the working tree (regenerated by slang).
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