fix: Prevent content scrolling behind main menu (part 1) (#35173)

app/javascript/mastodon/containers/mastodon.jsx

@@ -18,6 +18,7 @@ import initialState, { title as siteTitle } from 'mastodon/initial_state';
 import { IntlProvider } from 'mastodon/locales';
 import { store } from 'mastodon/store';
 import { isProduction } from 'mastodon/utils/environment';
+import { BodyScrollLock } from 'mastodon/features/ui/components/body_scroll_lock';
 
 const title = isProduction() ? siteTitle : `${siteTitle} (Dev)`;
 
@@ -58,6 +59,7 @@ export default class Mastodon extends PureComponent {
                 <ScrollContext shouldUpdateScroll={this.shouldUpdateScroll}>
                   <Route path='/' component={UI} />
                 </ScrollContext>
+                <BodyScrollLock />
               </Router>
 
               <Helmet defaultTitle={title} titleTemplate={`%s - ${title}`} />