ci: publish the Docker image to GHCR from Actions

Pushing to ghcr.io from a laptop needs a PAT with write:packages, which nobody
should have to create and store. Actions' automatic GITHUB_TOKEN already carries
that permission, so the build runs on GitHub's hardware and pushes from there.

Triggers on any v* tag and on manual dispatch. Frees ~25GB of preinstalled
toolchains first — the image is ~11GB and a stock runner only has ~14GB free on
/, so the build would otherwise die on disk space. amd64 only: emulating arm64
under QEMU for a nine-project install blows past the job time limit.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: ZD Studios

.github/workflows/docker-publish.yml

@@ -0,0 +1,82 @@
+name: Publish Docker image to GHCR
+
+# Builds the image on GitHub's runners and pushes it to ghcr.io.
+#
+# This exists because pushing from a laptop needs a Personal Access Token with
+# `write:packages`. Actions gets an automatic GITHUB_TOKEN that already has it —
+# see `permissions:` below — so nobody has to create or store a PAT.
+
+on:
+  push:
+    tags: ["v*"]          # every release tag publishes a matching image
+  workflow_dispatch:       # ...and you can run it by hand from the Actions tab
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: ${{ github.repository }}
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write      # this is what replaces the PAT
+
+    steps:
+      # The image is ~11GB. A stock runner has ~14GB free on /, which is not
+      # enough, so reclaim the preinstalled toolchains we don't use first.
+      - name: Free up disk space
+        run: |
+          echo "before:"; df -h / | tail -1
+          sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc \
+                      /usr/local/share/boost /usr/local/lib/node_modules \
+                      /opt/hostedtoolcache/CodeQL "$AGENT_TOOLSDIRECTORY" || true
+          sudo apt-get clean
+          docker image prune -af || true
+          echo "after:"; df -h / | tail -1
+
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - name: Log in to GHCR
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Docker metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=ref,event=tag
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=raw,value=latest,enable={{is_default_branch}}
+            type=raw,value=latest,enable=${{ startsWith(github.ref, 'refs/tags/v') }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          # linux/amd64 only: this image installs nine projects, and emulating
+          # arm64 under QEMU pushes the build past the runner's time limit.
+          platforms: linux/amd64
+          provenance: false
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+      - name: Summary
+        run: |
+          echo "### Image published :whale:" >> $GITHUB_STEP_SUMMARY
+          echo '```bash' >> $GITHUB_STEP_SUMMARY
+          echo "docker pull ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest" >> $GITHUB_STEP_SUMMARY
+          echo '```' >> $GITHUB_STEP_SUMMARY
+          echo "Make it public: repo → Packages → aios → Package settings → Change visibility" \
+            >> $GITHUB_STEP_SUMMARY