This panel only appears when you open the page with your private
?admin= URL — bookmark that link so it's just a click away.
Additions here only live in this browser tab. To make them visible to
everyone: copy the JSON above, paste it over the DATA
constant near the top of this file's source, then commit and push to
your GitHub Pages repo. Files uploaded from your device are embedded
directly in that JSON (no separate repo upload needed) — keep uploads
under a few MB each, since large files make the page heavier. For
bigger files, use the URL/path option and host the file elsewhere.