System prompt support!

I've finally come to adding system prompt support! This allows this project to very easily work with many of your favourite chat apps more seamlessly, and especially with coding applications. More importantly, the Codex CLI system prompt, which cannot be removed, doesn't seem to cause any visible degradation in my small testing with code quality or failing tool calls, etc.

Currently, only a Mac build will be available to ensure everything works as required, and soon I will release a full release including this along with a few other QoL features. You are still free to run the flask server yourself on windows or linux while waiting, as that contains the new changes.