QEMU arm64 Rust builds took 60+ min and timed out in CI. Now the Docker
job downloads the pre-built release binaries and packages them directly.
- Dockerfile.ci: slim image for CI (downloads pre-built binaries)
- Dockerfile: full source build for local dev (unchanged build stage)
- Both use ubuntu:24.04 (GLIBC 2.39 matches CI build environment)
- Multi-arch manifest combines amd64 + arm64 images
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
