?open= now also accepts an absolute path on the page's own origin, fetched
with the page's scheme, so a self-hosted setup that serves SolidCraft and
other tools under one origin can link a design on a LAN without a public
HTTPS address. Absolute URLs keep the HTTPS-only rule (a URL on the page's
own origin is also accepted), redirects must end on HTTPS or the same
origin, and protocol-relative, dot-segment, backslash and control-character
values are refused.