Implement MCNS v1: custom Go DNS server replacing CoreDNS

Replace the CoreDNS precursor with a purpose-built authoritative DNS
server. Zones and records (A, AAAA, CNAME) are stored in SQLite and
managed via synchronized gRPC + REST APIs authenticated through MCIAS.
Non-authoritative queries are forwarded to upstream resolvers with
in-memory caching.

Key components:
- DNS server (miekg/dns) with authoritative zone handling and forwarding
- gRPC + REST management APIs with MCIAS auth (mcdsl integration)
- SQLite storage with CNAME exclusivity enforcement and auto SOA serials
- 30 tests covering database CRUD, DNS resolution, and caching

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

go.mod

@@ -0,0 +1,34 @@
+module git.wntrmute.dev/kyle/mcns
+
+go 1.25.7
+
+require (
+	git.wntrmute.dev/kyle/mcdsl v1.0.0
+	github.com/go-chi/chi/v5 v5.2.5
+	github.com/miekg/dns v1.1.66
+	github.com/spf13/cobra v1.10.2
+	google.golang.org/grpc v1.79.3
+	google.golang.org/protobuf v1.36.11
+)
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	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/ncruces/go-strftime v1.0.0 // indirect
+	github.com/pelletier/go-toml/v2 v2.3.0 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	github.com/spf13/pflag v1.0.9 // indirect
+	golang.org/x/mod v0.33.0 // indirect
+	golang.org/x/net v0.50.0 // indirect
+	golang.org/x/sync v0.19.0 // indirect
+	golang.org/x/sys v0.42.0 // indirect
+	golang.org/x/text v0.34.0 // indirect
+	golang.org/x/tools v0.42.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20251202230838-ff82c1b0f217 // indirect
+	modernc.org/libc v1.70.0 // indirect
+	modernc.org/mathutil v1.7.1 // indirect
+	modernc.org/memory v1.11.0 // indirect
+	modernc.org/sqlite v1.47.0 // indirect
+)