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.

modules/core/default.nix

@@ -25,6 +25,7 @@
     ./user.nix
     ./ventoy.nix
     ./virtualbox.nix
+    ./virualization.nix
     ./xdg.nix
     ./xserver.nix
     ./zram.nix

modules/core/packages/appimages/helium.nix

@@ -4,8 +4,8 @@
   fetchurl,
 }: let
   pname = "helium";
-  version = "0.14.3.1";
-  hash = "sha256-umRDXcHlDRDWpdP4wxr81q+cUXkjiIxyg2AcJRFQaMA=";
+  version = "0.14.4.1";
+  hash = "sha256-91hO0NtjUxEZwUyMYe7RD1RfFIelYa8ExzLKRsLaZZo=";
 
   src = fetchurl {
     url = "https://github.com/imputnet/helium-linux/releases/download/${version}/helium-${version}-x86_64.AppImage";

modules/core/virualization.nix

@@ -0,0 +1,18 @@
+{
+  lib,
+  config,
+  ...
+}: {
+  options.virualization.enable = lib.mkEnableOption "Enable QEMU/KVM";
+
+  config = lib.mkIf config.virualization.enable {
+    virtualisation.libvirtd.enable = true;
+
+    programs.virt-manager.enable = true;
+
+    services = {
+      qemuGuest.enable = true;
+      spice-vdagentd.enable = true;
+    };
+  };
+}