Add GitHub Actions workflow

.github/workflows/ci.yml

@@ -0,0 +1,49 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  release:
+    types: [ published ]
+
+jobs:
+
+  build:
+    name: Build Image
+
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v27
+        with:
+          nix_path: nixpkgs=channel:nixos-23.11
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Login to GitHub container registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build image
+        run: |
+          nix build
+
+      - name: Load image and store ID
+        id: image
+        run: |
+          image_id=$(docker load < result | sed -n 's/^Loaded image: //p')
+          echo "image_id=${image_id}" >> "$GITHUB_OUTPUT"
+
+      - name: Print image ID
+        run: |
+          echo "${{ steps.image.outputs.image_id }}"