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/migrate.go

@@ -0,0 +1,46 @@
+package db
+
+import (
+	mcdsldb "git.wntrmute.dev/kyle/mcdsl/db"
+)
+
+// Migrations is the ordered list of MCNS schema migrations.
+var Migrations = []mcdsldb.Migration{
+	{
+		Version: 1,
+		Name:    "zones and records",
+		SQL: `
+CREATE TABLE IF NOT EXISTS zones (
+    id          INTEGER PRIMARY KEY,
+    name        TEXT NOT NULL UNIQUE,
+    primary_ns  TEXT NOT NULL,
+    admin_email TEXT NOT NULL,
+    refresh     INTEGER NOT NULL DEFAULT 3600,
+    retry       INTEGER NOT NULL DEFAULT 600,
+    expire      INTEGER NOT NULL DEFAULT 86400,
+    minimum_ttl INTEGER NOT NULL DEFAULT 300,
+    serial      INTEGER NOT NULL DEFAULT 0,
+    created_at  TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+    updated_at  TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now'))
+);
+
+CREATE TABLE IF NOT EXISTS records (
+    id         INTEGER PRIMARY KEY,
+    zone_id    INTEGER NOT NULL REFERENCES zones(id) ON DELETE CASCADE,
+    name       TEXT NOT NULL,
+    type       TEXT NOT NULL CHECK (type IN ('A', 'AAAA', 'CNAME')),
+    value      TEXT NOT NULL,
+    ttl        INTEGER NOT NULL DEFAULT 300,
+    created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+    updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+    UNIQUE(zone_id, name, type, value)
+);
+
+CREATE INDEX IF NOT EXISTS idx_records_zone_name ON records(zone_id, name);`,
+	},
+}
+
+// Migrate applies all pending migrations.
+func (d *DB) Migrate() error {
+	return mcdsldb.Migrate(d.DB, Migrations)
+}