v0.22.0 — Measurements without a terminal

• A Tools tab with the measurements that used to need a terminal. Off by default;
  switch it on under Settings → Does it work?. It runs three analyses that so far only
  existed as scripts: how fast a recognition is, how well each person is covered, and why
  events yield no usable face.
• This is not a convenience wrapper around the scripts — it could not be. scripts/ is not
  in the app image at all (the Dockerfile ships app/ and static/), and the delay
  measurement read journalctl, which does not exist in a container without systemd. For
  anyone running FaceID as a Home Assistant app, those analyses were unreachable, not just
  inconvenient.
• The delay measurement therefore uses a different source than the script: the history
  instead of the log. The event's start time is in the Frigate event id anyway, and the
  moment the name went out is in the history entry — so it needs neither the log nor camera
  access, and answers instantly.
• Recognitions from a history scan are excluded from the delay figures rather than silently
  averaged in; they lag their event by weeks and would wreck every median. The count of
  what was dropped is shown.
• Corrected: there is no 3-second floor. README and the notification blueprint said the
  name takes 3 seconds at the very best, "because that is how long Frigate takes to produce
  the first snapshot". The new tool made it checkable, and 18% of recognitions land below
  that, the fastest in 0.8s. The old figure was the median of first attempts in an older
  sample, written up as a physical limit. Both measurement paths — the log-based script and
  the history — now agree: median 8-9s, fastest around 1s, and the floor varies per event.
  Clocks were compared between Frigate and the container first; they match to the second.
• The history no longer prints a similarity of 1.0 as if it meant something. Every such
  entry was a face that had since been assigned, so it is one of that person's reference
  photos and matches itself. It now reads "now assigned: ", without a number.
• retry_seconds: 1.2 (down from 2.5) is confirmed to have worked: attempt 2 went from a
  median of 6.5s to 4.0s.
• Two long-standing bugs in the background jobs, found while reviewing the new one and
  fixed for the history scan and the calibration analysis as well:
  • A failing import inside a worker killed the thread before the finally that clears the
    running flag. The job then stayed "running" forever and every later start answered 409 already running until a service restart — with that message as the only clue, pointing
    at everything except the real cause. Verified by breaking the import on purpose.
  • Starting a job checked the running flag and set it in two separate steps, so two
    simultaneous starts could both get past the guard. Now held under one lock.