feat: add Axis::None for hidden dimensions with implicit aggregation

Categories on the None axis are excluded from the grid and cell keys.
When evaluating cells, values across hidden dimensions are aggregated
using a per-measure function (default SUM). Adds evaluate_aggregated
to Model, none_cats to GridLayout, and 'n' shortcut in TileSelect.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/view/axis.rs

@@ -6,6 +6,7 @@ pub enum Axis {
     Row,
     Column,
     Page,
+    None,
 }
 
 impl std::fmt::Display for Axis {
@@ -14,6 +15,7 @@ impl std::fmt::Display for Axis {
             Axis::Row => write!(f, "Row ↕"),
             Axis::Column => write!(f, "Col ↔"),
             Axis::Page => write!(f, "Page ☰"),
+            Axis::None => write!(f, "None ∅"),
         }
     }
 }

src/view/layout.rs

@@ -27,6 +27,8 @@ pub struct GridLayout {
     pub page_coords: Vec<(String, String)>,
     pub row_items: Vec<AxisEntry>,
     pub col_items: Vec<AxisEntry>,
+    /// Categories on `Axis::None` — hidden, implicitly aggregated.
+    pub none_cats: Vec<String>,
 }
 
 impl GridLayout {
@@ -46,6 +48,11 @@ impl GridLayout {
             .into_iter()
             .map(String::from)
             .collect();
+        let none_cats: Vec<String> = view
+            .categories_on(Axis::None)
+            .into_iter()
+            .map(String::from)
+            .collect();
 
         let page_coords = page_cats
             .iter()
@@ -77,6 +84,7 @@ impl GridLayout {
             page_coords,
             row_items,
             col_items,
+            none_cats,
         }
     }
 

src/view/types.rs

@@ -148,12 +148,13 @@ impl View {
         self.col_offset = 0;
     }
 
-    /// Cycle axis for a category: Row → Column → Page → Row
+    /// Cycle axis for a category: Row → Column → Page → None → Row
     pub fn cycle_axis(&mut self, cat_name: &str) {
         let next = match self.axis_of(cat_name) {
             Axis::Row => Axis::Column,
             Axis::Column => Axis::Page,
-            Axis::Page => Axis::Row,
+            Axis::Page => Axis::None,
+            Axis::None => Axis::Row,
         };
         self.set_axis(cat_name, next);
         self.selected = (0, 0);
@@ -302,9 +303,17 @@ mod tests {
     }
 
     #[test]
-    fn cycle_axis_page_to_row() {
+    fn cycle_axis_page_to_none() {
         let mut v = view_with_cats(&["Region", "Product", "Time"]);
         v.cycle_axis("Time");
+        assert_eq!(v.axis_of("Time"), Axis::None);
+    }
+
+    #[test]
+    fn cycle_axis_none_to_row() {
+        let mut v = view_with_cats(&["Region", "Product", "Time"]);
+        v.set_axis("Time", Axis::None);
+        v.cycle_axis("Time");
         assert_eq!(v.axis_of("Time"), Axis::Row);
     }
 
@@ -351,7 +360,7 @@ mod prop_tests {
         fn each_category_on_exactly_one_axis(cats in unique_cat_names()) {
             let mut v = View::new("T");
             for c in &cats { v.on_category_added(c); }
-            let all_axes = [Axis::Row, Axis::Column, Axis::Page];
+            let all_axes = [Axis::Row, Axis::Column, Axis::Page, Axis::None];
             for c in &cats {
                 let count = all_axes.iter()
                     .filter(|&&ax| v.categories_on(ax).contains(&c.as_str()))
@@ -377,7 +386,7 @@ mod prop_tests {
         fn set_axis_updates_axis_of(
             cats in unique_cat_names(),
             target_idx in 0usize..8,
-            axis in prop_oneof![Just(Axis::Row), Just(Axis::Column), Just(Axis::Page)],
+            axis in prop_oneof![Just(Axis::Row), Just(Axis::Column), Just(Axis::Page), Just(Axis::None)],
         ) {
             let mut v = View::new("T");
             for c in &cats { v.on_category_added(c); }
@@ -392,7 +401,7 @@ mod prop_tests {
         fn set_axis_exclusive(
             cats in unique_cat_names(),
             target_idx in 0usize..8,
-            axis in prop_oneof![Just(Axis::Row), Just(Axis::Column), Just(Axis::Page)],
+            axis in prop_oneof![Just(Axis::Row), Just(Axis::Column), Just(Axis::Page), Just(Axis::None)],
         ) {
             let mut v = View::new("T");
             for c in &cats { v.on_category_added(c); }