Layout starter prompt card action without image

[compulim]

Changelog Entry

Fixed

• (Experimental) Added pre-chat message with starter prompts in Fluent UI, in PR #5255 and #5263, by @compulim

Description

Fixes starter prompts without image should not leave a gutter for the image.

Design

Specific Changes

• Updated starter prompts card action with new CSS class to remove the image gutter

• I have added tests and executed them locally
• 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)

[OEvgeny]

Looks good, I think we should rely on actual DOM structure for applying CSS styles though: this makes us to not duplicate conditions and also makes markup structure a source of truth for our styles, which is extremely good for cases where grid is involved at least.