Fix async peer LLM token lookup, duplicate token bug, and improve async message view

[sethbern]

This PR fixes a few issues with the async peer LLM feature and cleans up the instructor view.

There was a duplicate token issue on the add token screen, the custom provider name input happened to share the token-input CSS class with the actual key field, so the submit handler was collecting it as a second token every time. The renamed class fixes this.

Fixed it so all messages from a student show up in order instead of just their last one in async peer when there is no llm. Also the LLM prompt has been updated.

[sethbern]

This also fixes issue #612

Fixes issue where the dropdown menu on the course home and course navigation showed up as white on white text.

[bnmnetp]

How are you forcing the course home page to be in dark mode?

I can see the problem you describe on RST built book pages where you turn on dark mode, but I believe that we have variables defined to use with the different modes. RST books are deprecated but I'm happy to merge PRs for them by others.

I would prefer this be done as a separate PR from the LLM token lookup. It makes it easier to track and easier to back out a merge if needed.

[sethbern]

@bnmnetp the dark mode fix has been moved to its own #1164. To answer your question: dark mode isn't being forced, it's user-activated via a toggle in the navbar that sets data-theme="dark" on the element. The styles just weren't covering that attribute for the dropdown menus.

[bnmnetp]

Thanks for the fix!!

I didn't expect that the custom option would be used (ever??!!) so I'm curious why you used this instead of openai?