Each target check now times out after 80% of the refresh interval, 24
seconds at 30 seconds, where it was capped at 3 seconds, so slow, far
targets are recorded with their real time. Rounds never overlap: a
round gives up the last round's checks if they are still waiting, which
happens only when a round starts early, after an interval change or
when the recovery probe finds a target answering. The probe still
checks every half second, giving up its previous checks, so they do not
pile up.
The frontend has its first unit tests, run by script/frontend-test with
Node's built-in test runner on a mocked clock. index.html now links
src/styles.css, which src/main.js imported, since Node cannot import
CSS.
Model: opus-5-5
