emacs: Match entire saved-search when computing search-view buffer name

I happen to have a lot of saved searches that are variants of the
tag:inbox search, (such as "tag:inbox and tag:notmuch"). The logic for
these was always matching inbox first, resulting in "[ inbox ] and
tag:notmuch" rather than "notmuch" as desired.

Anchor the regular expression on both ends to make it look harder for
the better match.