"discovery: mDNS/DNS-SD peer discovery; dynamic upstream management"

Allows ncro instances to discover each other dynamically without static
configuration and enables a peer-to-peer style (hello funny cube) mesh
where nodes share cached builds locally instead of all hitting upstream
caches.

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I7d723876c6816cb6aaaf3fe14cb24a426a6a6964

go.mod

@@ -3,6 +3,7 @@ module notashelf.dev/ncro
 go 1.25.7
 
 require (
+	github.com/grandcat/zeroconf v1.0.0
 	github.com/prometheus/client_golang v1.23.2
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0
@@ -14,6 +15,7 @@ require (
 
 require (
 	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cenkalti/backoff v2.2.1+incompatible // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
@@ -21,6 +23,7 @@ require (
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/miekg/dns v1.1.27 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.4 // indirect
@@ -37,8 +40,10 @@ require (
 	github.com/vmihailenco/tagparser/v2 v2.0.0 // indirect
 	go.yaml.in/yaml/v2 v2.4.3 // indirect
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
+	golang.org/x/crypto v0.48.0 // indirect
+	golang.org/x/net v0.50.0 // indirect
 	golang.org/x/sys v0.41.0 // indirect
-	golang.org/x/text v0.32.0 // indirect
+	golang.org/x/text v0.34.0 // indirect
 	golang.org/x/tools v0.42.0 // indirect
 	google.golang.org/protobuf v1.36.11 // indirect
 	modernc.org/libc v1.69.0 // indirect