Have chat entry and display respect ASCII trees

[cfdude]

A user in discord has requested this feature: https://discord.com/channels/1332146336664915968/1345091796501270588

The highlights of this request are:
Chat input destroys indentation hierarchy within ``` fencing.

It is useful to communicate directory structure with the LLM by using ASCII trees, but the chat trims the leading characters, at least when they are displayed in the chat.

I think [having the chat] respecting ASCII trees would be very narrow focus. ... What I was thinking is that if it respected Markdown fencing for code blocks and strings, then the user could at least see code blocks that match. It's sort of important for Python, for instance, and other whitespace sensitive structures.