[Bug] Web chat does not render Markdown in agent messages

[arefbehboudi]

Agent responses containing Markdown (bold, lists, code blocks, tables)
are displayed as raw text instead of being rendered.

Expected: **bold** renders as bold, code blocks get formatting, lists are readable.
Actual: Raw Markdown syntax is visible in the chat bubble.

Fix is frontend-only — parse agent message content with a Markdown
library (e.g. marked.js via CDN) before inserting into the DOM.
User messages must stay as plain text.