Inconsistent Mention Parsing between EmbeddedChat and Rocket.Core Chat

Description:

There is a difference in how user mentions are parsed and rendered in EmbeddedChat compared to the main Rocket.Chat core.

In Core Chat, a mention directly enclosed with parentheses (@username) is rendered as plain text and does not trigger a mention notification or highlight. However, in EmbeddedChat, the same pattern is parsed as a valid User Mention, displaying the mention tag.

Steps to reproduce:

1. Open Rocket.Chat Core.
2. Send a message: (@username)
3. Observe that it renders as plain text: (@username)
4. Open EmbeddedChat connected to the same server.
5. Observe the same message. Result: EmbeddedChat renders it as a mention tag: (@username)

Expected behavior:

EmbeddedChat should match Rocket.Chat core behavior. Mentions inside parentheses should be treated as plain text or at least be consistent across clients.

Actual behavior:

The Mentions Sidebar (which lists all messages where the user is mentioned) correctly excludes these messages. This confirms that the server (Core) correctly identifies that (@username) is not a mention. The issue is strictly isolated to the client side rendering in the chat view of EmbeddedChat, which visually formats the text as a mention tag even though it is not treated as one by the system logic.

EmbeddedChat

Rocket.Chat

No file or test is named in the issue. Start by tracing EmbeddedChat's client-side chat rendering for mentions and compare its handling of (@username) with Rocket.Chat core; done means the text remains plain and does not display a mention tag.