Fix local config system

[404Wolf]

In light of #220:

We already have support for local config already! But nobody uses it and it is broken. If you try to update a value that is already set in global config in your local config, it errors, saying that it is already set. I just removed all of this logic, since it seems like it just makes things more complicated for no reason. If you try to set something that's already set it should just overwrite it to the new value, even if it is the same value as before.

Two issues:

• I'm a bit concerned about is people mistakenly commiting their local configs with their apiKey to git. I added a tiny helper that says "do you want us to add it to your gitignore" when they add their apiKey, but really it might already be tracked. Any ideas here?
• Small thing, but zod removed .deepPartial() and I can't really find any suggested alternatives. https://www.npmjs.com/package/zod-deep-partial seems to do the trick. I kinda don't love this dep, maybe we can vendor just the object handling piece, or maybe it doesn't matter.

[tmcw]

Nice - yeah, I think that vendoring that third-party dep makes a lot of sense. Looked around and it doesn't seem like switching validators would be an easy fix - arktype and effect schema don't seem to have deepPartial either.

I'm a bit concerned about is people mistakenly commiting their local configs with their apiKey to git.

Recommending .gitignore feels like the most we can do without being too magic or overbearing.