Make new browser reloads recognize current model (fixes #4843)

[cyberfox]

This fixes a long-standing UI bug #4843 the simplest way possible.

Essentially instead of just giving the model name as the value, which then gets cached and not replaced...ever, we give a Callable that returns the current model name so each time it generates the UI for a 'new' browser session, it updates the model name to be whatever's current.

Before this change, the displayed name would always be the default after a reload or when hit by another browser. I ran into it most often when switching between iPhone and desktop. With this change it shows the latest model loaded. And yes, the pull request is a hundred times longer than the change, but it took me hours to get here. 🤣

Checklist:

• I have read the Contributing guidelines.

[oobabooga]

That's a very clever solution. Well done.

[djbritt]

Is this issue relevant to when I have a session going, and I reload the browser, I get this error

Could not find the character "[]" inside characters/. No character has been loaded - file File "/home/user1/git/oobabooga-4-1-24/modules/chat.py", line 673, in load_character

I am on ubuntu 22.04