web/settings: space settings list rows 8px apart like figma
figma lays every one of these cards out as [row, separator, row] with an 8px
auto-layout gap, so there is only ever one value to express: py-2 on each row,
which is the spacing unit that resolves to 8px on the default scale. that
leaves the card py-1, the rest of the 12px figma puts between its edge and the
first row.
with a single value the gap variant has nothing left to vary, so it folds into
the base and SettingsSection loses the rowGap prop it only forwarded. the repo
pages drop gap="3", which was 6px either side of the hairline, and the lists
reached through SettingsSection drop 4px either side — both now 8.
figma still draws 16px on the keys, emails, knots and spindles cards and 12px
on hooks; those follow the new single value here.
Signed-off-by: eti <eti@eti.tf>