The ChatGPT app only has the nifty "works with any app" feature if you're on the Plus plan and doesn't support other models. Chital looks very nice and is admirably tiny (3.6MB unzipped!) but doesn't have the editor integration at all, as far as I can tell.

MindMac is an example of an app that meets all the criteria, but for more than it seems like such an app should cost.