Add cross-distribution OS package installers (Arch PKGBUILD, Debian control, RPM spec) and restructure tests.

Remove deprecated AUR and Ansible requirements installers.
Introduce Nix init + wrapper scripts and full packaging (Arch/DEB/RPM).
Associated conversation: https://chatgpt.com/share/693476a8-b9f0-800f-8e0c-ea5151295ce2

package-manager.spec

@@ -0,0 +1,58 @@
+Name:           package-manager
+Version:        0.1.1
+Release:        1%{?dist}
+Summary:        Wrapper that runs Kevin's package-manager via Nix flake
+
+License:        MIT
+URL:            https://github.com/kevinveenbirkenbach/package-manager
+Source0:        %{name}-%{version}.tar.gz
+
+BuildArch:      noarch
+Requires:       nix
+
+%description
+This package provides the `pkgmgr` command, which runs Kevin's package
+manager via a Nix flake:
+
+  nix run "github:kevinveenbirkenbach/package-manager#pkgmgr" -- ...
+
+Nix is the only runtime dependency and must be initialized on the
+system to work correctly.
+
+%prep
+%setup -q
+
+%build
+# No build step required
+:
+
+%install
+rm -rf %{buildroot}
+install -d %{buildroot}%{_bindir}
+install -d %{buildroot}%{_libdir}/package-manager
+
+# Wrapper
+install -m0755 scripts/pkgmgr-wrapper.sh %{buildroot}%{_bindir}/pkgmgr
+
+# Shared Nix init script
+install -m0755 scripts/init-nix.sh %{buildroot}%{_libdir}/package-manager/init-nix.sh
+
+%post
+if [ -x %{_libdir}/package-manager/init-nix.sh ]; then
+    %{_libdir}/package-manager/init-nix.sh || true
+else
+    echo ">>> Warning: %{_libdir}/package-manager/init-nix.sh not found or not executable."
+fi
+
+%postun
+echo ">>> package-manager removed. Nix itself was not removed."
+
+%files
+%doc README.md
+%license LICENSE
+%{_bindir}/pkgmgr
+%{_libdir}/package-manager/init-nix.sh
+
+%changelog
+* Sat Dec 06 2025 Kevin Veen-Birkenbach <info@veen.world> - 0.1.1-1
+- Initial RPM packaging for package-manager