Bold formatting not split at emoji boundaries causing duplicate text on web

## Problem

  When combining bold formatting with emojis (e.g., `*bold 😀 text*`), the web platform displays duplicate emoji characters. This also causes cursor positioning issues.

  ### Steps to Reproduce

  1. Open the web app
  2. In the chat composer, type: `*bold 😀 text*`
  3. Observe duplicate emoji in the rendered output