Adds a third "small" size to the Nova Focus Timer widget on New Tab, alongside
the existing medium and large sizes. Small is a compact, vertically centered
layout matching the Figma design: a progress ring with the play/pause control,
a single editable duration row when idle, and just the ring plus remaining time
while running or paused. It has no manual Focus/Break toggle (the timer
auto-cycles) and no reset control; the completion celebration reuses the shared
animation but shows only the headline.
The classic (non-Nova) layout is untouched.
Differential Revision: https://phabricator.services.mozilla.com/D309283
Nina Pypchenko
f967e650a0