chore(packaging): docker-compose + Caddyfile for ODoH relay deploy

Two-container deploy: Caddy terminates TLS (auto-provisions Let's
Encrypt via ACME) and reverse-proxies to a Numa relay on an internal
Docker network. The relay never reads sealed payloads; Caddy's
access log is discarded so per-request observability doesn't defeat
the oblivious property.

Validated against Hetzner CX22 + DNS at odoh-relay.numa.rs:
- TLS-ALPN-01 challenge succeeded on first attempt
- /health returned the relay's counter block
- End-to-end ODoH client → relay → Cloudflare works

Operators only need to: set a DNS A record, edit Caddyfile's hostname,
docker compose up -d. README walks through the steps and the DNSCrypt
v3/odoh-relays.md submission to claim a public listing.

packaging/relay/docker-compose.yml

@@ -0,0 +1,26 @@
+services:
+  numa-relay:
+    image: ghcr.io/razvandimescu/numa:latest
+    command: ["relay", "8443", "0.0.0.0"]
+    restart: unless-stopped
+    networks: [internal]
+
+  caddy:
+    image: caddy:2
+    ports:
+      - "80:80"
+      - "443:443"
+    volumes:
+      - ./Caddyfile:/etc/caddy/Caddyfile:ro
+      - caddy_data:/data
+      - caddy_config:/config
+    restart: unless-stopped
+    depends_on: [numa-relay]
+    networks: [internal]
+
+networks:
+  internal:
+
+volumes:
+  caddy_data:
+  caddy_config: