web/components: use inset shadow only on raised buttons
the star button renders both in the repo header, where it is a raised
default button, and inside repo cards, where the card already carries
the elevation — so the caller decides via a prop instead of the
component hardcoding it. the profile rss link is flat for the same
reason.
the repo header fork group follows the design system segmented control:
the leading segment is default + inset shadow, the fork count segment is
ghost.
Signed-off-by: eti <eti@eti.tf>