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/db/db.go

@@ -0,0 +1,23 @@
+package db
+
+import (
+	"database/sql"
+	"fmt"
+
+	mcdsldb "git.wntrmute.dev/kyle/mcdsl/db"
+)
+
+// DB wraps a SQLite database connection.
+type DB struct {
+	*sql.DB
+}
+
+// Open opens (or creates) a SQLite database at the given path with the
+// standard Metacircular pragmas: WAL mode, foreign keys, busy timeout.
+func Open(path string) (*DB, error) {
+	sqlDB, err := mcdsldb.Open(path)
+	if err != nil {
+		return nil, fmt.Errorf("db: %w", err)
+	}
+	return &DB{sqlDB}, nil
+}