EVO-70 Tier 0: conditionalize drain-email-outbox pg_cron — EXISTS-guard so empty ticks fire zero HTTP/Vercel

EVO-70 fleet Tier-0 (ship same-day, reversible, DB-lane, no app deploy). Wrap pg_cron jobid6 net.http_get in a plpgsql IF-guard fn that fires ONLY when work is due. Predicate MUST byte-match worker eligibility: status='pending' AND COALESCE(nextAttemptAt, createdAt) <= now() (backoff-leak catch — bare status='pending' would re-fire on future-scheduled retry rows). Empty/not-due tick -> zero HTTP round-trip, zero Vercel invocation. Keep */5 as retry timer in T0. One migration, reversible. This cron is PERMANENT durability recovery — never retired even after Tier 1 (pg_net tables are UNLOGGED/beta).