Fixes login failing silently on authenticated + private deployments
served over plain HTTP (e.g. Tailscale, LAN). Users can sign up and
sign in, but the session cookie is rejected by the browser so they
are immediately redirected back to the login page.
Better Auth defaults to __Secure- prefixed cookies with the Secure
flag when NODE_ENV=production. Browsers silently reject Secure cookies
on non-HTTPS origins. This detects when PAPERCLIP_PUBLIC_URL uses
http:// and sets useSecureCookies: false so session cookies work
without HTTPS.
ad55af04cc