feat: Add markdown rendering and styling to chat messages using marked and dompurify.

[HarixhKumawat]

Resolves #8
added chat-markdown and markdown files.

• chat-markdown.ts: added an observer on the chat element. It loops through the messages, finds the one that changed, and replaces it with the newly formatted version.
• markdown.ts: this file contains the rules of the markdown and sanitizes using the dompurify to make sure no XSS attack is possible.