feat(claude): add nodejs and OMC_PLUGIN_ROOT for oh-my-claudecode support

Adds nodejs to home packages (required by claude-code and OMC HUD/npm
plugins) and sets OMC_PLUGIN_ROOT env var pointing to the flake input.

home.nix

@@ -29,6 +29,7 @@
     gnomeExtensions.arc-menu
     freecad
     gtk3  # Provides org.gtk.Settings.FileChooser schema for FreeCAD
+    nodejs  # Required by claude-code and oh-my-claudecode (HUD, npm plugins)
   ];
 
   # --------------------------
@@ -289,6 +290,7 @@
       };
       env = {
         CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS = "1";
+        OMC_PLUGIN_ROOT = "${oh-my-claudecode}";
       };
       teammateMode = "tmux";
     };