0.18.1

Two fixes found by jig-site's fourth round: the probe misread a <details>
menu, and A-05 missed an arrow that renders as an emoji.

Fixed

• The probe reads a <details> menu the way the browser shows it. On
  jig-site's Reference it reported a working phone menu as broken, and
  jig verdicts refused a correct P-14 verdict on the strength of it. Four
  defects, each now covered by a browser test:

  • Where the banner's menu is hidden at a width, the probe took the next
    disclosure in some other <nav> (a docs rail's section tree) as the menu,
    and reported "a menu button beside links that already show". A menu the
    page names, or one in its banner, is now the only candidate once it exists.
  • A closed <details> hides its content with content-visibility in
    Chromium, which still gives its links boxes, so the closed menu's links
    counted as showing and opening it "showed no more links". Visibility now
    also asks checkVisibility().
  • A label swapped with CSS ("Menu" to "Close") keeps both words in
    textContent; the label is now read from the rendered text.
  • A native <summary> has no aria-expanded attribute; its expanded state
    is its <details>'s open, which is what assistive technology is given.

  Probe files are now version 6, so earlier ones are re-recorded.

• A-05 catches an arrow that turns into an emoji. ↔ ↕ ↖ ↗ ↘ ↙ ↩ ↪ ▶ ◀
  are text by default but have an emoji form, and the detector skipped the
  whole arrow block so prose arrows would not fire. jig-site marked its
  external links with <span aria-hidden="true">↗</span>, which some platforms
  draw as a colour emoji, and check --all and three critiques passed it. One
  of these characters now fires when it stands alone as an icon (the whole
  content of an element, or a pseudo-element's content) without U+FE0E. The
  same arrow in a sentence still does not.