Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `README.md`:
  Upstream changed their README, we have our own.
  Kept ours.
- `app/helpers/application_helper.rb`:
  Minor code style fix upstream, on a line that is different in glitch-soc
  due to the different theming system.
  Applied the code style fix to our own code.
- `app/views/settings/preferences/appearance/show.html.haml`:
  Code style fix on a line next to lines exclusive to glitch-soc.
  Applied upstream changes.
- `yarn.lock`:
  Upstream updated a dependency textually close to a glitch-soc-only
  dependency.
  Updated the dependency like upstream did.

app/views/layouts/mailer.html.haml

@@ -35,7 +35,7 @@
                 %tbody
                   %tr
                     %td.content-cell.content-end
-                      != "  "
+                      != '  '
                   %tr
                     %td.blank-cell.footer
                       .email-row