#53 FTX-53: Expiry worker loop

ACTIVE-status decisions past expires_at batch FOR UPDATE SKIP LOCKED -> terminalize(timed_out) or policy auto-approve (OP-EXP-1, UB-EXP-2); soft-warning reminders (EV-EXP-1). Race test: approve-vs-expire -> exactly one terminal side effect (dedup_key proves). Phase 3.