OpenPose Editor 0.3.1 for Forge Classic 2.28.1

I really liked this editor, but a few important parts no longer worked reliably with sd-webui-forge-classic 2.28.1. I migrated and hardened it with a little help from AI, and I hope this build is useful to other people in the community. This release fixes canvas-edge points and detector confidence, secures the iframe and FastAPI data exchange, fixes background-image races, and replaces the old updater with a bounded atomic installer. The attached dist.zip is the exact frontend expected by version 0.3.1 of the fork.