feat: add view code dialog

[OEvgeny]

Fixes #

Changelog Entry

• Added code viewer dialog with syntax highlighting, in PR #5335, by @OEvgeny

Description

Adds a dialog to view code snippets with syntax highlighting in chat messages. The feature focuses on improving code readability and maintaining good performance through selective language imports.

Design

• Dialog opens when clicking the code button
• Uses Shiki for syntax highlighting with lazy loading
• Supports JavaScript, TypeScript, and Python initially
• Fetches code from the basedOn if available in Message metadata

Specific Changes

• Added ActivityViewCodeButton and CodeContent components
• Integrated Shiki with GitHub light/dark themes
• Added code icon button to message footer
• Added AI-generated code warning notice
• Added test coverage and localization strings

-

• 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)