Add Docker deployment via Gitea Actions host-mode runner

Containerize the app (Dockerfile, docker-compose.yaml) and add a CI
deploy job that syncs the checkout to /srv/docker/maptool and runs
docker compose directly, using the runner's new "host" execution
label to reach the host's Docker daemon and filesystem.

.dockerignore

@@ -0,0 +1,5 @@
+.git
+data
+.gitea
+.claude
+.ruby-lsp