feat: push Docker image to GitHub Container Registry on release

Replace generic registry secrets with ghcr.io using the built-in
GITHUB_TOKEN. Use docker/metadata-action for automatic semver tagging.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -20,31 +20,33 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Extract version from tag
-        id: version
-        run: echo "VERSION=${GITHUB_REF#refs/tags/}" >> $GITHUB_OUTPUT
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/${{ github.repository }}
+          tags: |
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=raw,value=latest
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
 
-      - name: Login to Container Registry
-        if: env.REGISTRY_URL != ''
+      - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
         with:
-          registry: ${{ secrets.REGISTRY_URL }}
-          username: ${{ secrets.REGISTRY_USER }}
-          password: ${{ secrets.REGISTRY_TOKEN }}
-        env:
-          REGISTRY_URL: ${{ secrets.REGISTRY_URL }}
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build and push Docker image
         uses: docker/build-push-action@v6
         with:
           context: .
-          push: ${{ secrets.REGISTRY_URL != '' }}
-          tags: |
-            ${{ secrets.REGISTRY_URL && format('{0}/crumbs:{1}', secrets.REGISTRY_URL, steps.version.outputs.VERSION) || '' }}
-            ${{ secrets.REGISTRY_URL && format('{0}/crumbs:latest', secrets.REGISTRY_URL) || '' }}
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
           cache-from: type=gha
           cache-to: type=gha,mode=max