Fixing "Selected tag uses an invalid operating system " error when deploying to Azure Container Apps

When deploying a Docker image to Azure Container Apps, a cryptic 'Selected tag uses an invalid operating system' error can occur. The root cause is Docker BuildKit's default provenance attestation, which adds an extra manifest entry with an empty OS field that Azure Container Apps cannot handle. The fix is to build with two flags: `--platform linux/amd64` to pin the target platform and `--provenance=false` to disable the problematic attestation metadata.