Get email campaign statistics

Returns aggregated statistics for one email campaign. By default (detailed omitted or not 'true') a flat summary is returned; with detailed=true a { global, steps } breakdown is returned. Statistics are computed on demand and cached. PITFALLS: when the campaign is not found the route answers 401 (not 404) with { error: 'Campaign not found' }; ANY internal error also answers 401 { error: 'You must be logged in' }. detailed is read as the string 'true'; any other value (including the boolean true serialised elsewhere) is treated as the summary. New integrations should use the multichannel /advanced campaign endpoints instead.