- garmin_sync_iter: sync gear registry from Garmin on every sync run and
resolve gear for each newly imported activity via get_activity_gear()
- POST /api/garmin/import-gear: one-time backfill that matches Garmin gear
activities to existing local activities by UTC timestamp (±60 s)
Matches the Strava sync table layout. Accumulates total_imported in
garmin_sync.json state on each sync run; admin API exposes last_sync_at
and total_imported from that file.