fix(pr): report checks like gh, exit 8 while they are pending

tea pr checks printed relative links, "Error: pull request checks have
not all succeeded" with exit 1 for checks that were only pending, and
nothing at all without checks. It now heads the table with a colored
verdict and "0 failing, 1 successful, and 2 pending checks", prints a
status icon and absolute links, and exits 8 while checks are pending
and 1 when one failed, without an Error line (D21). clierr.Quiet
carries such an exit code past main without a message. Without checks
it says "no checks reported for pull request alice/x#8".

--watch redraws the summary in place on a terminal, and an expired
--timeout reads "timed out after 3s waiting for 2 pending checks". The
pull request argument is optional, and --web opens the pull request.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/app_test.go

@@ -457,7 +457,6 @@ const (
 	pr attachment upload
 	pr attachment view
 	pr checkout
-	pr checks
 	pr clean
 	pr close
 	pr comment create