add docker configuration and gitea workflow for automated image builds

Introduce a multi-stage Dockerfile, docker-compose setup, and a Gitea Actions workflow to automate building and pushing images to the registry. The configuration includes an entrypoint script for persistent logging and a .dockerignore to optimize the build context.

docker/entrypoint.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+set -e
+
+mkdir -p /logs
+
+# Run the app and tee output to both stdout (for `docker logs`) and a
+# persistent log file inside the mounted volume.
+exec ./emly-api 2>&1 | tee -a /logs/app.log