Add native RTL support for Markdown rendering

What variant of Codex are you using?

IDE Extension

What feature would you like to see?

Current behavior

Markdown messages are always rendered LTR.

Problem

Persian and Arabic users cannot read long answers comfortably.

Expected behavior

If the detected language is RTL, automatically set:

direction: rtl;
text-align: start;

or provide a user setting:

☑ Enable RTL rendering

Additional information

_No response_