Invite tokens now include a redirect claim so the verify endpoint
can distinguish them from regular login tokens. Only invite links
redirect to wiki.ghostguild.org; normal logins go to /members.
Invite emails now include both plain text and HTML versions. The
{loginLink} placeholder renders as a styled button in HTML email
clients. Other URLs in the template are auto-linked. The auth verify
endpoint redirects to wiki.ghostguild.org instead of /members.
