OP said, in their post, they “Couldn't find one”

It’s totally fine to build your own implementation of something, especially if it’s for personal use or you’re not charging. OP is pitching a paid product. It’s not okay to ignore the sea of competitors and pitch your product on HN with a marketing blurb that isn’t true.

Anybody can slap together a chat UI and integrate a few LLM APIs. We need more than that if you’re charging money.