feat: add provenance attestations

.github/workflows/next.yaml

@@ -46,6 +46,7 @@ jobs:
 
       - name: Build and push Docker image
         uses: docker/build-push-action@v6
+        id: push
         with:
           context: .
           file: ./Dockerfile
@@ -55,3 +56,10 @@ jobs:
           platforms: linux/amd64, linux/arm64
           cache-from: type=gha
           cache-to: type=gha,mode=max
+      - name: Attest
+        uses: actions/attest-build-provenance@v2
+        id: attest
+        with:
+          subject-name: ghcr.io/${{ github.repository }}
+          subject-digest: ${{ steps.push.outputs.digest }}
+          push-to-registry: true