Only the 8084 forward is exposed; the desktop GUI runs inside the
container netns and is internal-only. Drop the now-unneeded
CUSTOM_HTTPS_PORT (no host-port conflict exists inside the netns).
lscr.io/linuxserver/calibre:9.15.0 (desktop build) running calibre-server
as the s6 main service on internal 8090 -> host 8084, auth-gated with a
plaintext userdb (mode 600) bootstrapped once by the deploy handler.
The desktop GUI is kept on 8080/8182, basic-authed with the same
credential pair via the machine-local env file.