fix: copilot header font

[OEvgeny]

Fixes #

Changelog Entry

• (Experimental) Expand Fluent theme support to activities and transcript, in PR #5258, by @OEvgeny
  • Fixed header font in copilot variant, in PR #5261, by @OEvgeny

Description

This PR addresses an issue with the font used in the header of the copilot variant in the Fluent UI theme's copilot variant. The change ensures that the header font is consistent with the primary font used throughout the Web Chat interface.

Specific Changes

• Updated ActivityDecorator.module.css to use the primary font variable for the activity decorator
• Updated snapshots to reflect the font change

-

-

• [x] I have added tests and executed them locally
• [x] I have updated CHANGELOG.md
• [ ] ~I have updated documentation~

Review Checklist

This section is for contributors to review your work.

• [ ] Accessibility reviewed (tab order, content readability, alt text, color contrast)
• [ ] Browser and platform compatibilities reviewed
• [ ] CSS styles reviewed (minimal rules, no z-index)
• [ ] Documents reviewed (docs, samples, live demo)
• [ ] Internationalization reviewed (strings, unit formatting)
• [ ] package.json and package-lock.json reviewed
• [ ] Security reviewed (no data URIs, check for nonce leak)
• [ ] Tests reviewed (coverage, legitimacy)