coredns: docker compose stack with Vultr zone import

- Auto plugin loads zones-prepared/*.zone (regex zone-name extraction)
- scripts/prepare-zones.sh transforms raw Vultr exports:
  * synthesizes SOA (omitted by Vultr; CoreDNS requires it)
  * prepends @ to leading-TAB apex lines to disambiguate owner inheritance
  * dot-terminates NS/MX/CNAME rdata so $ORIGIN doesn't double-suffix
- DNS_PORT defaults to 1053 (5353=avahi, 53=libvirt dnsmasq on this host)
- Forwards non-authoritative queries to 1.1.1.1/1.0.0.1/9.9.9.9
- Makefile targets: prep, up, down, reload, test, logs
- 91 zones loaded

docker-compose.yml

@@ -0,0 +1,20 @@
+services:
+  coredns:
+    image: ${COREDNS_IMAGE}
+    container_name: coredns
+    restart: unless-stopped
+    command: ["-conf", "/etc/coredns/Corefile"]
+    ports:
+      - "${DNS_PORT}:53/udp"
+      - "${DNS_PORT}:53/tcp"
+      - "${METRICS_PORT}:9153/tcp"
+      - "${HEALTH_PORT}:8080/tcp"
+    volumes:
+      - ./Corefile:/etc/coredns/Corefile:ro
+      - ./zones-prepared:/zones:ro
+    healthcheck:
+      test: ["CMD", "wget", "-qO-", "http://127.0.0.1:8080/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 10s