v5 documented PORT as a legacy alias for FRONTEND_PORT. v6 dropped the
fallback silently, so an install configured with PORT=8080 upgrades to
v6 and comes up on 7655 with no explanation, unreachable behind its
existing port mapping or reverse proxy.
Honor PORT again at lowest precedence (FRONTEND_PORT wins when both are
set) and log a deprecation warning at startup, mirroring the existing
legacy DISABLE_AUTH handling. Document PORT as deprecated in
CONFIGURATION.md and note the compatibility behavior in the v6
changelog.
rcourtman
43bc15c12f