Start Segment Endpoint

Re-enable a campaign that was stopped via /stop — the status-aware inverse, so a re-checked campaign actually resumes whatever it was doing: • listening → resume (→ outreach), gated by the affordability check; • review → un-freeze the auto-approve countdown (fresh window); • discovery → re-kick the discovery pipeline (idempotent). Already-running (outreach) / terminal (archived) / error → no-op.

Thin adapter: the orchestration lives in segment_control.start_campaign (shared with the public API); this endpoint only translates the cookie session into an org_id and maps domain errors to HTTP.