Change public accounts pages to mount the web UI (#19319)

* Change public accounts pages to mount the web UI

* Fix handling of remote usernames in routes

- When logged in, serve web app
- When logged out, redirect to permalink
- Fix `app-body` class not being set sometimes due to name conflict

* Fix missing `multiColumn` prop

* Fix failing test

* Use `discoverable` attribute to control indexing directives

* Fix `<ColumnLoading />` not using `multiColumn`

* Add `noindex` to accounts in REST API

* Change noindex directive to not be rendered by default before a route is mounted

* Add loading indicator for detailed status in web UI

* Fix missing indicator appearing while account is loading in web UI

app/views/statuses/show.html.haml

@@ -2,7 +2,7 @@
   = t('statuses.title', name: display_name(@account), quote: truncate(@status.spoiler_text.presence || @status.text, length: 50, omission: '…', escape: false))
 
 - content_for :header_tags do
-  - if @account.user&.setting_noindex
+  - if @account.user_prefers_noindex?
     %meta{ name: 'robots', content: 'noindex, noarchive' }/
 
   %link{ rel: 'alternate', type: 'application/json+oembed', href: api_oembed_url(url: short_account_status_url(@account, @status), format: 'json') }/