Fix follow/unfollow buttons on public profile (fixes #7036) (#7040)

* Fix follow/unfollow buttons on public profile

- Present non-logged users with web+mastodon:// URLs for remote accounts
- Present logged-in users with appropriate links (authorize_follows and
  remote_unfollows) for remote accounts

* Do not cache rendered cards if user is logged in

app/controllers/concerns/remote_account_controller_concern.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module RemoteAccountControllerConcern
+  extend ActiveSupport::Concern
+
+  included do
+    layout 'public'
+    before_action :set_account
+    before_action :check_account_suspension
+  end
+
+  private
+
+  def set_account
+    @account = Account.find_remote!(params[:acct])
+  end
+
+  def check_account_suspension
+    gone if @account.suspended?
+  end
+end