ranges:dates samples each active group's posting dates from the news
server (group_dates) and estimates every range's date (ranges.est_date).
ranges:capture --from --to marks a window's ranges of every group for the
corpus. The corpus fill takes capture ranges in priority order, done ones
too, and remembers complete ones (ranges.stored_at).
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
