purgeContentRows deleted a lineup group's lineupItems and lineupAgents rows
all at once. A trashed page whose groups hold tens of thousands of them
broke Convex's per-transaction limits on every run, and since the daily
purge always starts from the oldest page, it stopped purging every page
trashed after it, for every user.

The side rows now share the run's budget with reference rows (200), and a
lineup row goes only once both side tables are empty for it; the purge
reschedules itself for the rest, as it already did for references.