ci: remove GitHub CI — native git.hanzo.ai + cd.hanzo.ai only

This workflow ran on a self-hosted actions-runner-controller pool. ARC is
decommissioned: CI executes inside git.hanzo.ai (Gitea Actions, .hanzo/workflows)
and delivery is cd.hanzo.ai reconciling the reviewed image pin in
hanzoai/universe. GitHub is a mirror and runs nothing.

Removed rather than repointed — there is no GitHub-side pool to move to, and
leaving it would keep ARC load-bearing.

.github/workflows/docker-publish.yml

@@ -1,27 +0,0 @@
-name: Docker Release
-
-on:
-  push:
-    branches: [main]
-    tags: ["v*"]
-  workflow_dispatch:
-
-concurrency:
-  group: docker-${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: false
-
-permissions:
-  contents: read
-  packages: write
-  id-token: write
-
-jobs:
-  docker:
-    uses: hanzoai/.github/.github/workflows/docker-build.yml@main
-    with:
-      image: ghcr.io/hanzoai/agent
-      context: control-plane
-      dockerfile: Dockerfile
-      platforms: linux/amd64
-      runner-amd64: '["hanzo-build-linux-amd64"]'
-    secrets: inherit