Mention autocomplete triggers on email addresses

The mention popup in ChatInput fires whenever you type @ after a space. Problem is, that also matches email addresses — typing something like contact admin @example.com pops up the member list and starts filtering against "example.com".

The trigger logic in useSearchMentionUser.js:23-26:

if (
  lastChar === '@' &&
  (message.length === 1 || message[message.length - 2] === ' ')
)

It checks "is this an @ after a space?" but doesn't try to figure out whether the user is mentioning someone or just typing an email.

Steps to reproduce:

1. Open EmbeddedChat in any room
2. In the message input, type contact admin @example.com
3. The mention popup appears as soon as you hit @
4. It filters members against "example.com"

Expected behavior:

Mention popup shouldn't fire when the user is typing an email address.

Actual behavior:

Popup fires on any @ preceded by a space. You have to dismiss it or ignore it while finishing the email.

Code reference:

packages/react/src/hooks/useSearchMentionUser.js:23-26

Start in packages/react/src/hooks/useSearchMentionUser.js:23-26 and inspect how the ChatInput trigger is detected after a space. Reproduce the email-address example in an EmbeddedChat room, then verify that the mention popup still appears for intended mentions but not while typing an email address.