The perf summary API only returned the last three non-empty buckets as
bare success rates, so the 24-slot status strip on model cards never lit
more than three bars and could not show hours without traffic.
Replace recent_success_rates with recent_success_series: one timestamped
point per hour that had requests, aligned to hour start regardless of
the configured bucket size. The badge now anchors its 24 slots to the
client's current hour and places each point by timestamp, leaving hours
without data gray.
