* Move the Nix bootstrap from *scripts/init-nix.sh* to *scripts/nix/init.sh* with split-out helpers in *scripts/nix/lib/*
* Update Arch/Debian/Fedora packaging hooks to call */usr/lib/package-manager/nix/init.sh*
* Keep bootstrap behavior the same while improving maintainability and reuse
https://chatgpt.com/share/693c7159-b340-800f-929e-2515eeb0dd03
Refactor CI to clearly separate virtualenv-based container tests from pure Nix flake tests across all distros (arch, debian, ubuntu, fedora, centos).
Introduce dedicated test-env-nix workflow and Makefile targets, rename former container tests to test-env-virtual, and update stable pipeline dependencies.
Improve Nix reliability in containers by fixing installer permissions and explicitly validating nix availability and version during image build and tests.
* Move Arch-specific ignore rules into `packaging/arch/.gitignore` and simplify top-level `.gitignore`/`.dockerignore`.
* Update Arch `PKGBUILD` to sync from the project root and drop `packaging/` from the installed tree.
* Fix OS-specific `package.sh` helpers to resolve the new `packaging/*` locations correctly for Arch, Debian/Ubuntu, Fedora, and CentOS.
