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/controllers/concerns/signature_verification.rb

@@ -138,7 +138,7 @@ module SignatureVerification
   end
 
   def signed_headers
-    signature_params.fetch('headers', signature_algorithm == 'hs2019' ? '(created)' : 'date').downcase.split(' ')
+    signature_params.fetch('headers', signature_algorithm == 'hs2019' ? '(created)' : 'date').downcase.split
   end
 
   def verify_signature_strength!