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/README.md

@@ -0,0 +1,48 @@
+# Numa ODoH Relay — Docker deploy
+
+Two-container deploy: Caddy terminates TLS (auto-provisioning a Let's Encrypt
+cert via ACME) and reverse-proxies to a Numa relay running on an internal
+Docker network. The relay never reads sealed payloads; Caddy never logs them.
+
+## Prerequisites
+
+- A host with public 80/443 reachable from the internet.
+- A DNS record (`A` or `AAAA`) pointing your chosen hostname at the host.
+- Docker + Docker Compose v2.
+
+## Configure
+
+Edit `Caddyfile` and replace `odoh-relay.example.com` with your hostname.
+That hostname is what ACME validates against and what ODoH clients will
+configure as their relay URL: `https://<hostname>/relay`.
+
+## Deploy
+
+```sh
+docker compose up -d
+docker compose logs -f caddy   # watch ACME provisioning
+```
+
+First boot takes a few seconds while Caddy obtains the cert. Subsequent
+restarts reuse the cached cert from the `caddy_data` volume.
+
+## Verify
+
+```sh
+curl https://<hostname>/health
+# ok
+# total 0
+# forwarded_ok 0
+# forwarded_err 0
+# rejected_bad_request 0
+```
+
+Then point any ODoH client at `https://<hostname>/relay` and watch the
+counters tick.
+
+## Listing on the public ecosystem
+
+DNSCrypt's [v3/odoh-relays.md](https://github.com/DNSCrypt/dnscrypt-resolvers/blob/master/v3/odoh-relays.md)
+is the canonical list. The pruned 2025-09-16 commit shows one public ODoH
+relay survived the cull — running this compose file doubles global supply.
+Open a PR there once your relay has been up for ~24 hours.