ADIF records frequently include operator commentary in the
<NOTES> field (multi-line, detailed) or <COMMENT> (short
one-liner). Now that contacts have a notes column, pass that
value through the import pipeline instead of dropping it.
Preference is NOTES over COMMENT to match the ADIF 3.1.4 spec's
intended split — NOTES is the richer field. Whitespace-only
values collapse to nil so a program that always emits a blank
NOTES tag doesn't fill every row with an empty string.
Tests cover NOTES capture, COMMENT fallback, NOTES-over-COMMENT
preference, and the absent-field nil case. ADIF upload blurb
lists the new carry-over so users see it before confirming.