v0.18.4

Fixed

• Gmail Android dark mode is modelled from the real app instead of a generic
  partial invert. On a real Gmail Android capture the old model agreed with
  the phone on 4 of 12 text-on-background swatches and 6 of 12 held-out ones;
  the new one agrees on 12 and 10. It no longer turns white button text dark
  or leaves grey footer text on dark grey, which raised dark-mode contrast
  errors on ordinary emails. It does catch what real Gmail Android breaks:
  dark text on a light-coloured button turns white (2.1:1 on amber). Known
  misses: a light grey darkens further than modelled, and one green text
  darkens. One phone, one app version; Gmail iOS is not measured yet.

• A Gmail wrapper rule meant for Gmail's own auto-links, such as
  u + #body a { color: inherit !important }, also matches the email's
  buttons and beats their inline colour and size. On real Gmail web it
  collapsed the main button in 11 of 20 emails of an agent benchmark. New
  style-survival rule gmail-wrapper-overrides-inline: an error when the
  rule's !important declarations override a button's inline values, a
  warning for plain links; rules under prefers-color-scheme are skipped,
  since Gmail never applies them. Checked against human grades of 239 real
  Gmail captures: errors on all 11 broken emails, none on one that holds.

• The Gmail wrapper selector matches any id or class on <body>, not only
  .body, and .menu + .x is no longer read as u + .x.

• The Gmail preview builds the wrapper the way Gmail does, inside <body>,
  so u + #body rules apply there. The <u> used to sit before <body>,
  where a browser moves it back in, and only for a .body class.