Before importing each Strava activity, build a set of existing timestamp
prefixes (YYYY-MM-DDTHHMMSSZ) from the activities directory. If the incoming
Strava activity matches an existing prefix, record its Strava ID as done and
skip — preventing duplicate entries when a FIT file and a Strava sync both
cover the same ride.
Also reports skipped-existing count in the summary line.
Davide Scaini