The golangci-lint binary was hardcoded as linux-amd64, causing Docker builds
to fail on arm64 hosts. The amd64 ELF binary cannot execute on aarch64,
producing a misleading shell syntax error during make check.
Use uname -m to detect the container architecture at build time and download
the matching binary. Both amd64 and arm64 SHA-256 hashes are pinned.
Closes#15
