The /contacts LiveTable export produces a 12-column CSV with label-style
headers (Station 1 / Grid 1 / QSO (UTC) / ...) in a different column
order plus extras (id, distance_km, hrrr_status, flagged_invalid,
inserted_at). The old positional import rejected it with "expected 6 or
7 columns, got 12".
Replace the positional parser with header-driven mapping:
- Parse the header row, normalize each cell (downcase + trim), and look
it up in an alias map that covers both the raw field names and the
export labels.
- Required columns: station1, station2, grid1, grid2, band, qso_timestamp
(mode stays optional). If any are missing the header, return
{:error, {:missing_required_columns, [...]}}.
- Unknown columns are silently ignored so the export's extras don't break
round-trip.
- Per-row validation stays the same (changeset errors still reported by
row number).
Existing 6- or 7-column positional CSVs that already have a header still
work — the header parser recognizes `station1`, `station2`, etc.
directly.