Add virtualization support and adjust defaults

- Disable printing by setting `printEnable = false`.
- Add a new `virualization` module enabling libvirtd, virt‑manager,
  qemuGuest and spice‑vdagentd; enable it on the desktop host.
- Change default applications: enable GIMP, disable Pixieditor.
- Bump Helium AppImage to version 0.14.4.1 with updated hash.
- Lower notification sound volume from 0.5 to 0.1.
- Refactor Bash and Fish aliases: `upd` now updates flakes,
  `upg` performs OS switch, and new helper aliases are added.

hosts/Garand-Laptop/system-modules.nix

@@ -4,6 +4,7 @@ _: {
   */
   docker.enable = true; # Docker: container runtime and management
   virtualbox.enable = false; # VirtualBox: PC emulator
+  virualization.enable = false; # GUI application for managing local and remote virtual machines through libvirt
   flatpak = {
     enable = true; # Flatpak: universal packaging system for Linux
     packages = {