web/settings: draw the settings list hairlines with divide-y

the three gap variants each repeated their own border-t and border colour on
an [&>*+*] selector; divide-y divide-border-default says it once in the base,
so a variant only has to carry spacing.

the spacing had to move with it. divide-y draws on the bottom of every row but
the last, where the old rule drew on the top of every row but the first, and
the rows carry min-h-8 — being border-box, that swallowed the old border and
top padding whole, so the hairline actually sat 12px under one row and 8px over
the next with an uneven 45/41px text pitch. giving each row half the gap as its
own padding, and leaving the card the rest of its 12px, puts the line where the
comment always claimed it was: 8/8 with an even 41px pitch. cards come out
8-11px shorter for it.

Signed-off-by: eti <eti@eti.tf>