When PicPeak runs behind NPM / Traefik / Caddy, the inner nginx receives
plain HTTP from the outer proxy. The previous `X-Forwarded-Proto $scheme`
therefore always forwarded "http" to the backend, even when the public URL
was HTTPS. Express has `trust proxy` enabled for loopback/linklocal, so
req.secure became false, the Secure cookie flag wasn't set, and generated
URLs (cookies, tokens) used http://.
Add a top-of-file `map` block that picks the incoming X-Forwarded-Proto
when present and falls back to `$scheme` for direct access. Applied to both
nginx.conf (bundled production image) and nginx.dev.conf.
Validated with `nginx -t` against nginx:1.28-alpine (the same image used
by Dockerfile.prod / Dockerfile).
Paul Nothaft
5488de3383