Get campaign performance stats

Returns campaign performance in one call: totals, per-A/B-variant results, per-sequence-step results, and a daily (UTC) time series. Sent and bounced count outbound emails; replied and positive count distinct leads; totals.meetings counts the campaign's leads with a booked meeting recorded (see POST /leads/{id}/meeting). Variant sent counts initial emails only, while steps attribute replies to the exact email that was answered. There is no opens metric anywhere in this response: Emailchaser does not track opens, so its absence is deliberate, not an omission.