ci: add GHCR container publish pipeline with semantic tags

Introduce a dedicated publish-containers workflow triggered after stable releases.
Unify container build and publish logic via scripts, add buildx-based multi-tag publishing,
default base image resolution, and Arch alias tags for latest/version/stable.

https://chatgpt.com/share/693c836b-0b00-800f-9536-9e273abd0fb5

.github/workflows/publish-containers.yml

@@ -0,0 +1,63 @@
+name: Publish container images (GHCR)
+
+on:
+  workflow_run:
+    workflows: ["Mark stable commit"]
+    types: [completed]
+
+jobs:
+  publish:
+    if: ${{ github.event.workflow_run.conclusion == 'success' }}
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout repository (with tags)
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          fetch-tags: true
+
+      - name: Checkout workflow_run commit
+        run: |
+          set -euo pipefail
+          git checkout -f "${{ github.event.workflow_run.head_sha }}"
+
+      - name: Compute version and stable flag
+        id: info
+        run: |
+          set -euo pipefail
+
+          SHA="$(git rev-parse HEAD)"
+          V_TAG="$(git tag --points-at "${SHA}" --list 'v*' | sort -V | tail -n1)"
+          [[ -n "$V_TAG" ]] || { echo "No version tag found"; exit 1; }
+
+          VERSION="${V_TAG#v}"
+
+          STABLE_SHA="$(git rev-parse -q --verify refs/tags/stable^{commit} 2>/dev/null || true)"
+          IS_STABLE=false
+          [[ "$STABLE_SHA" == "$SHA" ]] && IS_STABLE=true
+
+          echo "version=${VERSION}" >> "$GITHUB_OUTPUT"
+          echo "is_stable=${IS_STABLE}" >> "$GITHUB_OUTPUT"
+
+      - uses: docker/setup-buildx-action@v3
+        with:
+          use: true
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Publish all images
+        run: |
+          set -euo pipefail
+          OWNER="${{ github.repository_owner }}" \
+          VERSION="${{ steps.info.outputs.version }}" \
+          IS_STABLE="${{ steps.info.outputs.is_stable }}" \
+          bash scripts/build/publish.sh