[FR] AI chat mention a page UI improvments

[richardshiue]

Description

Even though we've disabled the mention a page feature recently, we plan to re-enable it in the future. Below are some aspects UI that could be improved when we get there:

• If there is a mention page in the input, ctrl + left or right arrow key to jump to the previous or next word doesn't behave correctly.
• Sometimes, the mention page menu after inserting "@" shows "no page results" when there are actually documents
• loading indicator for sending a long message could use some visual upgrade
• add some space between consecutive mentioned pages in the ai prompt input
• styling for mentioned pages in user-sent messages.

Impact

AI Chat users

Additional Context

No response