Both additive on top of the existing presets::N0 pkarr+DNS path.
mDNS lets peers on the same LAN find each other with zero internet
roundtrip — useful for home WiFi, conference rooms, ICE-train WiFi,
or any environment where pkarr/DNS isn't reachable. Pkarr-DHT adds
a third discovery path that doesn't depend on n0.computer's DNS
server being reachable; default relay_only filter keeps direct
addrs out of the public DHT.

All three providers run in parallel; lookup results union. If any
one is reachable, peers find each other.