fix(git): parse co-author trailers that are not RFC 5322 addresses (#39076)

Bot co-authors like `dependabot[bot]` render as one long string with the
email inside the name, and never get truncated, so they overflow the
column.

Co-author idents are parsed with `net/mail`, but a git ident isn't an
email address. `mail.ParseAddress` rejects the whole value when the name
holds characters RFC 5322 reserves, like a `[bot]` suffix or a comma, so
the error branch keeps the raw trailer as the display name and throws
the address away. No address means no `mailto:` link, and the anchor is
what `.avatar-stack-names` truncates.

So parse the angle-addr ourselves when `net/mail` won't take it.
Splitting on the last `<` is safe because git strips angle brackets from
idents. The bare-name branch gets the class too.

Fixes https://github.com/go-gitea/gitea/issues/38949

web_src/css/avatar.css

@@ -16,6 +16,7 @@ img.ui.avatar,
 }
 
 .avatar-stack-names > a.muted,
+.avatar-stack-names > .avatar-stack-name,
 .avatar-stack-names > .avatar-stack-popup-trigger {
   overflow: hidden;
   text-overflow: ellipsis;