Agent chat: show the agent's answers as Markdown (#1778)

Thanks @Rec0iL.

docs/agent-chat.md

@@ -149,6 +149,9 @@ The agent reaches the open design only through SolidCraft's own tools (the
   a single undo step, named after your message. The conversation shows *N changes, one undo
   step* with **Undo these changes** while nothing else has happened since.
 - **Tool cards:** each tool call shows as a card with its state; click it to see what it returned.
+- **Formatted text:** the agent's answers show as Markdown: headings, lists, quotes, code blocks
+  (with **Copy**), bold, italic, `code` and links (web links only; each link is a button that opens
+  it in your browser). What you type, and the agent's thoughts, stay plain text.
 - **Attach view:** tick it to send a picture of the current view with your message, for agents
   that take pictures.