Merge commit '877090518682b6c77ba9bdfa0231afd56daec44d' into glitch-soc/merge-upstream

Conflicts:
- `app/models/concerns/user/has_settings.rb`:
  Not a real conflict, upstream added a setting textually close to a glitch-soc one.
  Added upstream's new setting.
- `app/views/settings/preferences/appearance/show.html.haml`:
  Not a real conflict, upstream added a setting textually close to a glitch-soc one.
  Added upstream's new setting.
- `config/routes.rb`:
  Upstream moved web app routes to `config/routes/web_app.rb`, while glitch-soc had
  an extra route.
  Moved the extra route to `config/routes/web_app.rb`.
- `spec/controllers/settings/preferences/appearance_controller_spec.rb`:
  This spec got converted to a system spec upstream.
  However, the theme setting works differently in glitch-soc, so the spec had been
  changed.
  Changed the corresponding system spec as well.

app/javascript/entrypoints/embed.tsx

@@ -60,6 +60,10 @@ window.addEventListener('message', (e) => {
 
   const data = e.data;
 
+  // Only set overflow to `hidden` once we got the expected `message` so the post can still be scrolled if
+  // embedded without parent Javascript support
+  document.body.style.overflow = 'hidden';
+
   // We use a timeout to allow for the React page to render before calculating the height
   afterInitialRender(() => {
     window.parent.postMessage(