fix: update font size of prompt when validated

[lucaseduoli]

This pull request includes several changes to the frontend components and styles to improve the consistency and appearance of the application. The most important changes include updates to class names and styles, as well as the introduction of a utility function for combining class names.

Component updates:

• src/frontend/src/components/common/sanitizedHTMLWrapper/index.tsx: Imported the cn utility function and updated the className property to use cn for combining class names. [1] [2]
• src/frontend/src/modals/promptModal/index.tsx: Modified the className property to remove the bg-muted class and add the m-0 class.

Style updates:

• src/frontend/src/modals/promptModal/utils/var-highlight-html.tsx: Removed the font-semibold class from the HTML string.
• src/frontend/src/style/applies.css: Added the font-semibold class to the .chat-message-highlight style.