Add a Traefik IP allowlist so *.falcon.pivoine.art rejects any source
outside the Tailscale/Headscale CIDR ranges, even though DNS still
resolves publicly. Pair it with a headscale MagicDNS override so
tailnet clients resolve the hostname straight to the VPS's tailscale
IP and route correctly.
Requires Docker's userland-proxy disabled on the VPS host
(/etc/docker/daemon.json) so Traefik sees real client source IPs
instead of the docker bridge gateway — done manually, not tracked
in this repo.
valknar