systemd-resolved listening on port 53 (even localhost-only) blocks
dnsmasq from binding to port 53 globally, causing DHCP to fail on reboot.
Created drop-in systemd-resolved-disable.conf to prevent the service from
listening on DNS. dnsmasq becomes the sole DNS+DHCP server on bridge br0.
Critical fix: without this, clients don't receive DHCP after reboot.
Verified: 5+ active DHCP leases, clients receiving 10.42.1.x addresses.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
