Fix repo hygiene, CI publishing, and healthcheck coverage

[treyyoder]

Summary

• .gitignore: split the garbled single pattern quakejsdocs (missing newline since creation) into quakejs and docs, so a local quakejs clone from the README's non-Docker instructions is actually ignored.
• .gitattributes: add *.cfg text eol=lf and normalize server.cfg line endings, so the one config file COPY'd into the image no longer varies by checkout platform.
• CI: the workflow now logs into Docker Hub and pushes treyyoder/quakejs:latest on pushes to master/main via docker/build-push-action; pull requests remain build-only. The previously-unused Buildx setup step is now actually used.
• Healthcheck: also verify the game server accepts TCP connections on 27960, not just Apache. Wrapped in an explicit bash -c because HEALTHCHECK shell-form commands run under /bin/sh (dash) at runtime — the Dockerfile SHELL instruction does not apply — and dash lacks bash's /dev/tcp.
• README: document that HTTP_PORT is the host-side port baked into the client page and must match the port mapping.

Before merging

Add repository secrets DOCKERHUB_USERNAME and DOCKERHUB_TOKEN (Docker Hub access token, read/write). Without them the push step fails on the first master build. Note: the current latest on Docker Hub dates from 2022-08-30 — the first successful merge will replace it.

Testing

Built the image locally and ran a container: HTTP 200, index.html host/port rewrite verified, game port accepting connections, and Docker's healthcheck reports healthy. The pre-fix /dev/tcp healthcheck was confirmed failing (exit 2 under dash) before the bash -c wrapper fixed it.

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