Build for amd+arm with same tag

So docker can auto-select based on system.

The issue is about creating a multi-architecture Docker image for the cairo-cli. Start by examining the existing Dockerfile and build scripts in the repository. Research how to build and push multi-arch images using Docker Buildx. The goal is to produce a single image tag that supports both amd64 and arm64 architectures, allowing Docker to auto-select.

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