Get campaign statistics

Retrieve the "Statistiques" report for a campaign: the four-tile cascade funnel (appelés → eus en ligne → réels échanges → leads chauds), two secondary tiles, the distribution of exchanges by outcome, the list of hot leads, and data-extraction coverage. All counts are over distinct E.164-normalized phone numbers, and the outcome-based categories derive exclusively from calls.outcome. Cascade percentages are null when their denominator is zero.