Feature: Make message showed as markdown in chat-plugin and copied as text

[zhogu]

This pull request enhances the chat message display in the ChatHistory.tsx component by improving the rendering of message content and adding a user-friendly copy-to-clipboard feature. The changes focus on better Markdown support, improved styling, and new interactivity for copying messages.

UI/UX Improvements:

• Added a copy-to-clipboard button that appears when hovering over a chat message, allowing users to easily copy the message content (including reasoning if present) to their clipboard.
• Improved message and reasoning rendering by replacing plain text with the CustomMarkdown component, enabling better Markdown formatting and display.
• Enhanced layout and styling for message containers, including better handling of overflow and maximum width for improved readability. [1] [2]

Code and Dependency Updates:

• Replaced the SigmaIcon import with ClipboardCopy from lucide-react to support the new copy feature, and removed unused icon imports.
• Introduced hover state management to control the visibility of the copy button.

[Copilot]

Pull Request Overview

This PR enhances the chat message display by adding markdown rendering support and a copy-to-clipboard feature. The changes improve the user experience by making messages more readable with proper markdown formatting and providing an easy way to copy message content.

• Added hover-triggered copy-to-clipboard functionality for chat messages
• Replaced plain text rendering with CustomMarkdown component for better formatting
• Improved styling and layout with better overflow handling

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