The proactive-nudge frequency gate only counted delivered push attempts. A
user with no push channel never wrote a delivered row, so the cap was inert
for them: every cron tick that hit a persistent trigger minted a fresh nudge
conversation in the rail.
Count a recently persisted nudge conversation toward the same rolling window
so the once-per-window contract holds regardless of push outcome. Add a
covering index on coach messages for the assistant-message scans the FAB poll
and the gate both run, and drop the unused providerType parameter from the
persistence helper now that the tag is fixed.
