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/Caddyfile

@@ -0,0 +1,15 @@
+odoh-relay.example.com {
+    handle /relay {
+        reverse_proxy numa-relay:8443
+    }
+    handle /health {
+        reverse_proxy numa-relay:8443
+    }
+    respond 404
+
+    # Per-request access logs defeat the point of an oblivious relay.
+    # Aggregate counters are exposed at /health on the relay itself.
+    log {
+        output discard
+    }
+}