v5.1.1 (#211)

• Features
  • A run that stops itself says why. OnlineSession.abort_reason carries the
    reason a lookup aborted the batch — most usefully a spent daily API quota,
    which stops a run nobody asked to stop. A caller's own cancel() leaves
    it unset, so an embedding application can tell a pause it initiated from
    one the server forced.
  • A search the daily-quota reserve stopped now reports Skipped with
    reason="quota_reserved" instead of passing for a source that looked and
    found nothing. Those two call for opposite handling: a comic nobody
    searched for should be tried again tomorrow, and one that genuinely missed
    should not. The matcher's own reason is now the exported constant
    SKIP_MATCHER_DECLINED alongside SKIP_QUOTA_RESERVED.