Use GIT_COMMIT_SHA env var instead of execSync for Docker compatibility

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

.github/workflows/docker.yml

@@ -61,5 +61,7 @@ jobs:
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
+          build-args: |
+            GIT_COMMIT_SHA=${{ github.sha }}
           cache-from: type=gha
           cache-to: type=gha,mode=max