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>

internal/grpcserver/zones.go

@@ -0,0 +1,134 @@
+package grpcserver
+
+import (
+	"context"
+	"errors"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	pb "git.wntrmute.dev/kyle/mcns/gen/mcns/v1"
+	"git.wntrmute.dev/kyle/mcns/internal/db"
+)
+
+type zoneService struct {
+	pb.UnimplementedZoneServiceServer
+	db *db.DB
+}
+
+func (s *zoneService) ListZones(_ context.Context, _ *pb.ListZonesRequest) (*pb.ListZonesResponse, error) {
+	zones, err := s.db.ListZones()
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to list zones")
+	}
+
+	resp := &pb.ListZonesResponse{}
+	for _, z := range zones {
+		resp.Zones = append(resp.Zones, zoneToProto(z))
+	}
+	return resp, nil
+}
+
+func (s *zoneService) GetZone(_ context.Context, req *pb.GetZoneRequest) (*pb.Zone, error) {
+	zone, err := s.db.GetZone(req.Name)
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "zone not found")
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to get zone")
+	}
+	return zoneToProto(*zone), nil
+}
+
+func (s *zoneService) CreateZone(_ context.Context, req *pb.CreateZoneRequest) (*pb.Zone, error) {
+	refresh := int(req.Refresh)
+	if refresh == 0 {
+		refresh = 3600
+	}
+	retry := int(req.Retry)
+	if retry == 0 {
+		retry = 600
+	}
+	expire := int(req.Expire)
+	if expire == 0 {
+		expire = 86400
+	}
+	minTTL := int(req.MinimumTtl)
+	if minTTL == 0 {
+		minTTL = 300
+	}
+
+	zone, err := s.db.CreateZone(req.Name, req.PrimaryNs, req.AdminEmail, refresh, retry, expire, minTTL)
+	if errors.Is(err, db.ErrConflict) {
+		return nil, status.Error(codes.AlreadyExists, err.Error())
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to create zone")
+	}
+	return zoneToProto(*zone), nil
+}
+
+func (s *zoneService) UpdateZone(_ context.Context, req *pb.UpdateZoneRequest) (*pb.Zone, error) {
+	refresh := int(req.Refresh)
+	if refresh == 0 {
+		refresh = 3600
+	}
+	retry := int(req.Retry)
+	if retry == 0 {
+		retry = 600
+	}
+	expire := int(req.Expire)
+	if expire == 0 {
+		expire = 86400
+	}
+	minTTL := int(req.MinimumTtl)
+	if minTTL == 0 {
+		minTTL = 300
+	}
+
+	zone, err := s.db.UpdateZone(req.Name, req.PrimaryNs, req.AdminEmail, refresh, retry, expire, minTTL)
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "zone not found")
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to update zone")
+	}
+	return zoneToProto(*zone), nil
+}
+
+func (s *zoneService) DeleteZone(_ context.Context, req *pb.DeleteZoneRequest) (*pb.DeleteZoneResponse, error) {
+	err := s.db.DeleteZone(req.Name)
+	if errors.Is(err, db.ErrNotFound) {
+		return nil, status.Error(codes.NotFound, "zone not found")
+	}
+	if err != nil {
+		return nil, status.Error(codes.Internal, "failed to delete zone")
+	}
+	return &pb.DeleteZoneResponse{}, nil
+}
+
+func zoneToProto(z db.Zone) *pb.Zone {
+	return &pb.Zone{
+		Id:         z.ID,
+		Name:       z.Name,
+		PrimaryNs:  z.PrimaryNS,
+		AdminEmail: z.AdminEmail,
+		Refresh:    int32(z.Refresh),
+		Retry:      int32(z.Retry),
+		Expire:     int32(z.Expire),
+		MinimumTtl: int32(z.MinimumTTL),
+		Serial:     z.Serial,
+		CreatedAt:  parseTimestamp(z.CreatedAt),
+		UpdatedAt:  parseTimestamp(z.UpdatedAt),
+	}
+}
+
+func parseTimestamp(s string) *timestamppb.Timestamp {
+	// SQLite stores as "2006-01-02T15:04:05Z".
+	t, err := parseTime(s)
+	if err != nil {
+		return nil
+	}
+	return timestamppb.New(t)
+}