Resume Segment Endpoint

Resume a paused Campaign through the shared start orchestration.

Only legal from listening. If targeting changed while paused, this moves the Campaign back to discovery and enqueues Retarget before any old outreach can resume; otherwise it resumes the prior lifecycle normally.

Refuses with 402 when the org can't afford even one more email — same Email Affordability Gate the sender-worker _precheck and POST /api/app-auto-gtm/segments/{id}/launch already share. Without this check, resuming a debt-paused or empty-wallet campaign would immediately stall again on the per-send precheck.