Return just a secondary email when searching users

Make clear the intention that, because of the unique constraint, there
can only be one record returned when doing an exact match on the email

app/models/user.rb

@@ -633,6 +633,7 @@ class User < ApplicationRecord
       matched_by_email_user_id = email_table
         .project(email_table[:user_id])
         .where(email_table[:email].eq(query))
+        .take(1) # at most 1 record as there is a unique constraint
 
       where(
         fuzzy_arel_match(:name, query)