chore: add Docker deployment behind Caddy

Build the static Next.js export in a reproducible container and expose it
through the existing Caddy network and upstream service name.

DEPLOYMENT.md

@@ -0,0 +1,23 @@
+# Deployment
+
+This project builds the Next.js static export in a Node container and serves the
+generated files from Nginx on port 80. The container joins the existing
+`caddy_proxy` Docker network under the `static-site` service name expected by
+Caddy.
+
+## Deploy or update
+
+From the project directory on the server, run:
+
+```sh
+docker compose up --build -d
+```
+
+The external `caddy_proxy` network must already exist and Caddy must be attached
+to it. No host port is published because Caddy is the public entry point and
+terminates TLS for `amiirkhl.ir` and `www.amiirkhl.ir`.
+
+If the previous `static-site` container was created from a different Compose
+project directory, remove that old stack once before the first deployment to
+avoid a Docker container-name conflict. Updates from this project then use only
+the command above.