A Lane's pace, its refusal backoff and whether its Site needs the browser were
only ever visible in the log. The admin page (issue #102) has to state them, so
the Poller keeps one snapshot per Lane.
- LaneState/Status (status.go) is the page's view of a Lane: due, gap, clamped,
refusing, browser.
- runOnce records a snapshot on every return path, including the pass that
refuses, so a cooling Lane does not read as one that never ran.
- Refusing is derived at snapshot read time from the backoff, not stored: a
Lane that cooled down between passes must report false without a new pass.
- LaneStatus reports only Sites that have completed a pass, so a fresh restart
renders "no data yet" instead of confident zeroes.
