Fix announcements with fully-qualified mention to local user crashing WebUI (#13164)

app/models/account.rb

@@ -478,7 +478,16 @@ class Account < ApplicationRecord
     def from_text(text)
       return [] if text.blank?
 
-      text.scan(MENTION_RE).map { |match| match.first.split('@', 2) }.uniq.map { |(username, domain)| EntityCache.instance.mention(username, domain) }
+      text.scan(MENTION_RE).map { |match| match.first.split('@', 2) }.uniq.map do |(username, domain)|
+        domain = begin
+          if TagManager.instance.local_domain?(domain)
+            nil
+          else
+            TagManager.instance.normalize_domain(domain)
+          end
+        end
+        EntityCache.instance.mention(username, domain)
+      end.compact
     end
 
     private