feat: add syntax highlighting for AI code responses #122

[Aryanbuha890]

Summary

This PR adds theme-aware, automated syntax highlighting to all AI code blocks within the application, closing #122.

Changes

• prismjs Integration: Integrated prismjs as a dependency on the frontend.
• Shared Markdown Component: Created a shared Markdown formatting component in Markdown.jsx that replaces duplicated formatting logic in ResponseOutput.jsx and HistoryPanel.jsx.
• Auto-Language Detection: Added a heuristic language detector fallback inside the Markdown component to automatically detect code language blocks missing an explicit specifier.
• Light/Dark Syntax Theme: Defined custom CSS variables in index.css for both light mode (:root) and dark mode ([data-theme="dark"]) matching PrismJS highlight classes. This allows code token colors to adapt seamlessly and match the application theme dynamically.

Closes #122