ci: add workflow to build cross-compiler Docker image

.github/workflows/build-cross-image.yml

@@ -0,0 +1,69 @@
+name: Build Cross-Compiler Image
+
+on:
+  workflow_dispatch:
+    inputs:
+      sdk_version:
+        description: 'macOS SDK version'
+        required: true
+        default: '26.1'
+      zig_version:
+        description: 'Zig version'
+        required: true
+        default: '0.14.0'
+      image_version:
+        description: 'Image version tag'
+        required: true
+        default: '1.0.0'
+
+env:
+  REGISTRY: ghcr.io
+  IMAGE_NAME: wailsapp/wails-cross
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+
+    steps:
+      - name: Checkout v3-alpha
+        uses: actions/checkout@v4
+        with:
+          ref: v3-alpha
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ${{ env.REGISTRY }}
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
+          tags: |
+            type=raw,value=latest
+            type=raw,value=${{ inputs.image_version }}
+            type=raw,value=sdk-${{ inputs.sdk_version }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v5
+        with:
+          context: v3/internal/setupwizard/docker
+          file: v3/internal/setupwizard/docker/Dockerfile.cross
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          build-args: |
+            ZIG_VERSION=${{ inputs.zig_version }}
+            MACOS_SDK_VERSION=${{ inputs.sdk_version }}
+            IMAGE_VERSION=${{ inputs.image_version }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max