feat(installer): add software-profile multi-select

- Add select_profiles step with gum choose --no-limit
- Implement state persistence and review for selected profiles
- Map profiles to home.packages and system-level toggles (Docker, Steam)
- Update generate_flake_config to emit profile-specific Nix snippets
- Fix duplicate environment.systemPackages in virtualization.nix
- Update ROADMAP.md

core/system/virtualization.nix

@@ -19,15 +19,18 @@ in
   # `nomarchy.system.virtualization.libvirt.enable = true;`. The user must
   # be in the `libvirtd` group to drive virsh / virt-manager.
   virtualisation.libvirtd.enable = lib.mkIf libvirt true;
-  environment.systemPackages = lib.mkIf libvirt (with pkgs; [
-    virt-manager
-    qemu
-    OVMF
-  ]);
 
   # Optional: Docker + docker-compose.
   virtualisation.docker.enable = lib.mkIf docker true;
-  environment.systemPackages = lib.mkIf docker (with pkgs; [
-    docker-compose
-  ]);
+
+  environment.systemPackages = lib.mkMerge [
+    (lib.mkIf libvirt (with pkgs; [
+      virt-manager
+      qemu
+      OVMF
+    ]))
+    (lib.mkIf docker (with pkgs; [
+      docker-compose
+    ]))
+  ];
 }