- Dockerfile: linux-headers-amd64 meta-package instead of pinned ABI;
remove DEBIAN_KERNEL_ABI build-arg (no longer needed at image build time)
- build-in-container.sh: drop --build-arg DEBIAN_KERNEL_ABI
- build.sh: apt-get update + detect ABI from apt-cache at build time;
auto-install linux-headers-<ABI> if kernel changed since image build
Image rebuild is now needed only when changing Go version or lb tools,
not on every Debian kernel point release.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
