Mention a user does not work at 0.11.5

If i click a user in my chat then i get into the input line „user:“, but if i send it to the chat, no mention is done. There is no highlight of the user nor the user gets any notification for it.

Start by reproducing the issue on Element iOS 0.11.5: select a user from a chat, send the inserted “user:” text, and observe the resulting message. Trace the mention handling from that interaction and verify that the sent message highlights the user and triggers the expected notification.

Written by the indexing model from the issue text.