psa_post_log: backfill via psa_connection, fallback to posted_by user
psa_member_mappings: backfill via psa_connection
notification_logs: backfill via notification_config
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Backfill from rater/user's account_id (not the step's account_id).
This is an explicit design decision — step rating data is attributed
to the account that performed the rating.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>