gogarx/matrix-photo-gallery ? reverse-engineered prompt

Build me a simple photo gallery web app that shows images posted in a Matrix room.

I want it to pull photo events from one or more Matrix rooms, save them locally, and display them in a clean grid where I can browse through the pictures easily. It should use thumbnails for faster loading, and if possible let the app use smaller local thumbnails during development so it feels snappy. I also want a basic backend that can import images from Matrix and connect to a MongoDB database, plus a frontend that lets me view the gallery in the browser.

Please make it easy to run locally with clear setup steps, and include whatever is needed to configure the Matrix username, password, room IDs, and database URL. If you need to look up current docs or best practices for Matrix integration, go ahead and do that.