Root cause of test accounts receiving the newsletter: LISTMONK_API_USER was
set EMPTY in the portal env - env-present beats the code default, so every
listmonk_sync authenticated with an empty user and 403'd silently. Fixed both
the env (set to portal-sync) and the code (empty env falls back to default).
New: listmonk_reconcile() - the Members list must mirror ACTIVE members.
Stale subscribers are removed: members marked inactive are taken off the list
(record kept as suppression marker); addresses that are not members at all
(test/deleted accounts) are deleted outright. Wired as step 4 of the nightly
membership sweep + POST /admin/newsletter/reconcile for on-demand runs.