feat(mibook): boot to terminal, launch KDE on demand

Add my.profiles.kde-desktop.startOnBoot (default true, no change for
existing consumers). When false, boot to multi-user.target, keep SDDM
out of any boot target's wants, and provide a 'desktop' command that
starts the display manager on demand. Enable this on mibook.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CfozKLQdUh5TzqyjSigLUx

machines/mibook/environments.nix

@@ -6,6 +6,7 @@ in
 {
   my.profiles = {
     kde-desktop.enable = true;
+    kde-desktop.startOnBoot = false;
     zsh.enable = true;
     apps = {
       desktop_apps = true;

modules/environments/kde-desktop/default.nix

@@ -11,17 +11,37 @@ in
 {
   options.my.profiles.kde-desktop = with lib; {
     enable = mkEnableOption "KDE Desktop Environment";
+    startOnBoot = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether the display manager (SDDM) starts automatically at boot.
+        When false, the system boots to a text console and KDE can be
+        launched on demand with the `desktop` command.
+      '';
+    };
   };
 
-  config = lib.mkIf cfg.enable {
-    services = {
-      displayManager.sddm.enable = true;
-      displayManager.sddm.wayland.enable = true;
-      desktopManager.plasma6.enable = true;
-    };
-    users.users.finn.packages = with pkgs; [
-      # Programms can be added here...
-      numix-icon-theme
-    ];
-  };
+  config = lib.mkIf cfg.enable (lib.mkMerge [
+    {
+      services = {
+        displayManager.sddm.enable = true;
+        displayManager.sddm.wayland.enable = true;
+        desktopManager.plasma6.enable = true;
+      };
+      users.users.finn.packages = with pkgs; [
+        # Programms can be added here...
+        numix-icon-theme
+      ];
+    }
+    (lib.mkIf (!cfg.startOnBoot) {
+      # Boot to a text console; SDDM stays installed but is not pulled in
+      # by any boot target. Launch KDE on demand with `desktop`.
+      systemd.services.display-manager.wantedBy = lib.mkForce [ ];
+      systemd.defaultUnit = lib.mkForce "multi-user.target";
+      environment.systemPackages = [
+        (pkgs.writeShellScriptBin "desktop" "exec sudo systemctl start display-manager.service")
+      ];
+    })
+  ]);
 }