Fold Health Connect heart rate like Apple Health

The nightly dense-intraday fold scanned Apple Health rows only, so the
per-minute heart rate a Health Connect import writes for the last 90 days
never aged into hourly means and every new export added another quarter
of raw samples.

The fold now walks each fold source in turn, Apple Health first and
unchanged, and folds Health Connect samples into hourly stats: rows under
their own source, deleting the raw rows outright. The folded_window rule
covers both sources for the hour window and looks a covering row up under
the sample's own source; the day window stays Apple Health only. The
Health Connect importer applies the same rule to raw samples, so an
export that still holds folded minutes does not put them back.

docs/integrations/health-connect.md

@@ -135,6 +135,12 @@ export again writes nothing; a newer export that overlaps an older one
 adds only what is new. A value that changed on the phone is updated;
 a value you deleted in HealthLog stays deleted.
 
+Heart rate imported per minute ages the way Apple Health heart rate
+does: once a minute is older than 90 days, the nightly pass folds its
+hour into one hourly mean and removes the minutes. A later import of
+an export that still holds those minutes leaves them out, so an hour
+is never counted twice.
+
 ## Privacy
 
 - The uploaded ZIP and the extracted database are deleted as soon as