sessions --format json --contributions attaches turn-granular segments
(day, task category, carried git branch, short-model costs, active PR set)
that partition each session, so a selection can sum its exact share (20 of
a session's 100) while aggregate totals reconcile. Legacy prLinks-only
transcripts carry the whole set with the approx even-split marker, matching
the by-PR report. The menubar payload's topSessions and project
sessionDetails now carry provider + sessionId (+ raw projectKey for
topSessions) so the desktop can open the exact session behind a row, and
topActivities carries the raw TaskCategory for chips. serve learns the
--contributions flag so the desktop's resident child can answer it.
