Show HN: Penmentor – Claude marks up your handwritten math like a teacher

Penmentor is a tool that integrates Claude, Gemini, or GPT with the xournal++ note-taking app to provide real-time feedback on handwritten math work, marking mistakes and correct steps directly on the page while offering hints rather than solutions. The tool aims to enhance learning by providing targeted feedback, practice exercises, and interactive 3Blue1Brown-style animations to help users understand mathematical concepts. It works as a plugin that requires one of several AI agents to be installed and logged in on the user's system.