lovasoa/dezoomify — reverse-engineered prompt

Build me a simple Dezoomify style web app. I want to paste the URL of an online zoomable image from a museum, gallery, map viewer, Google Arts and Culture, IIIF page, Zoomify, Deep Zoom, OpenSeadragon, or similar viewer, and have the app find the image tiles, download them, stitch them together in the browser, and show me the full resolution image so I can save it.

Keep the interface simple, with one URL box, a start button, clear progress while tiles load, and useful error messages if the site or format is not supported. Include a generic mode where I can enter a tile URL pattern if automatic detection does not work. If the browser blocks requests from other sites, add a small proxy endpoint so the app can still fetch the tiles.

Please make it work as a mostly static JavaScript and HTML app, with canvas used for assembling the final image. Look up current docs online if needed.