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/javascript/mastodon/features/account/components/header.js

@@ -270,7 +270,9 @@ class Header extends ImmutablePureComponent {
     const content         = { __html: account.get('note_emojified') };
     const displayNameHtml = { __html: account.get('display_name_html') };
     const fields          = account.get('fields');
-    const acct            = account.get('acct').indexOf('@') === -1 && domain ? `${account.get('acct')}@${domain}` : account.get('acct');
+    const isLocal         = account.get('acct').indexOf('@') === -1;
+    const acct            = isLocal && domain ? `${account.get('acct')}@${domain}` : account.get('acct');
+    const isIndexable     = !account.get('noindex');
 
     let badge;
 
@@ -373,6 +375,7 @@ class Header extends ImmutablePureComponent {
 
         <Helmet>
           <title>{titleFromAccount(account)}</title>
+          <meta name='robots' content={(isLocal && isIndexable) ? 'all' : 'noindex'} />
         </Helmet>
       </div>
     );