Commit list display tweaks (#14043)

- Make plain <pre> inherit our monospace fonts, overriding fomantic's
  css reset which means expanded commit messages now follow the font
  settings.
- Adjust link styling and keyword highlighting in commit message
- Consolidate .commit-summary styles to single selector group

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/less/_base.less

@@ -150,6 +150,7 @@ textarea {
   font-family: var(--fonts-regular);
 }
 
+pre,
 code,
 kbd,
 samp {