Replace actions/checkout, setup-go, upload-artifact with an inline git
clone and a committed packwiz binary (tools/packwiz), so the workflow
needs no outside network beyond the docker image pull and a clone from
the instance itself. Release step (tag-gated) unchanged.
Replace server-side BlueMap 5.7 with Dynmap 3.7-beta-8 to cut web-map
tile storage down to explored chunks only. Updates MapLink client config
(Dynmap / :8123), docker-compose port 8100->8123, and README.
