Switch favicon to a black-on-white variant

Regenerate the full favicon set with the Cozystack icon as a black glyph
on a white square (replacing the previous white-on-#1a1a1a variant).

File names and pixel dimensions are unchanged, so favicons.html,
site.webmanifest and browserconfig.xml need no edits. The safari
pinned-tab mask (and its `color=` link) is left as-is.

Signed-off-by: Viktoriia Kvapil <bisunviktoria@gmail.com>

Author: Viktoriia Kvapil