bitEngine Hub firmware updates

Static files served at https://updates.bitengine.tech/hub/ via GitHub Pages. bitEngine Hub gateways fetch hub/manifest.json when the user presses Check for updates, then download the signed image it points to and verify the RSA-3072 signature before installing.

• hub/manifest.json — one version only; regenerated with tools/make_manifest.py in the firmware repo, never edited by hand.
• hub/bitengine-v<version>.bin — signed firmware images. Keep at least the previous version.

Do not rename hub/ or manifest.json — the URL is compiled into every shipped gateway.