fix(model): initialize virtual categories with Axis::None

Ensure that virtual categories (_Index, _Dim, _Measure) are registered in
the default view with Axis::None. This prevents potential panics when
calling axis_of on these categories and allows users to move them to a
specific axis manually.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (gemma-4-31B-it-UD-Q4_K_XL.gguf)

src/model/types.rs

@@ -61,15 +61,10 @@ impl Model {
             measure_agg: HashMap::new(),
             formula_cache: HashMap::new(),
         };
-        // Add virtuals to existing views (default view).
-        // Start in records mode; on_category_added will reclaim Row/Column
-        // for the first two regular categories.
         for view in m.views.values_mut() {
             view.on_category_added("_Index");
             view.on_category_added("_Dim");
             view.on_category_added("_Measure");
-            view.set_axis("_Index", crate::view::Axis::Row);
-            view.set_axis("_Dim", crate::view::Axis::Column);
         }
         m
     }
@@ -866,6 +861,17 @@ mod model_tests {
         let _ = m.active_view();
     }
 
+    /// improvise-kos: virtual categories must be registered in the default view
+    /// at Axis::None so they don't panic on axis_of and can be moved by the user.
+    #[test]
+    fn new_model_registers_virtuals_in_default_view() {
+        let m = Model::new("Test");
+        let v = m.active_view();
+        assert_eq!(v.axis_of("_Index"), Axis::None);
+        assert_eq!(v.axis_of("_Dim"), Axis::None);
+        assert_eq!(v.axis_of("_Measure"), Axis::None);
+    }
+
     #[test]
     fn add_category_creates_entry() {
         let mut m = Model::new("Test");