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/ui/app.rs

@@ -402,7 +402,8 @@ impl App {
             // yy = yank current cell
             ('y', KeyCode::Char('y')) => {
                 if let Some(key) = self.selected_cell_key() {
-                    self.yanked = self.model.evaluate(&key);
+                    let layout = GridLayout::new(&self.model, self.model.active_view());
+                    self.yanked = self.model.evaluate_aggregated(&key, &layout.none_cats);
                     self.status_msg = "Yanked".to_string();
                 }
             }
@@ -1111,6 +1112,19 @@ impl App {
                 }
                 self.mode = AppMode::Normal;
             }
+            KeyCode::Char('n') => {
+                if let Some(name) = cat_names.get(cat_idx) {
+                    command::dispatch(
+                        &mut self.model,
+                        &Command::SetAxis {
+                            category: name.clone(),
+                            axis: Axis::None,
+                        },
+                    );
+                    self.dirty = true;
+                }
+                self.mode = AppMode::Normal;
+            }
             _ => {}
         }
         Ok(())
@@ -1386,7 +1400,7 @@ impl App {
                     Some(k) => k,
                     None => return false,
                 };
-                let s = match self.model.evaluate(&key) {
+                let s = match self.model.evaluate_aggregated(&key, &layout.none_cats) {
                     Some(CellValue::Number(n)) => format!("{n}"),
                     Some(CellValue::Text(t)) => t,
                     None => String::new(),
@@ -1608,7 +1622,7 @@ impl App {
             AppMode::CategoryAdd { .. } => "Enter:add & continue  Tab:same  Esc:done — type a category name",
             AppMode::ItemAdd { .. } => "Enter:add & continue  Tab:same  Esc:done — type an item name",
             AppMode::ViewPanel => "jk:nav  Enter:switch  n:new  d:delete  Esc:back",
-            AppMode::TileSelect { .. } => "hl:select  Enter:cycle  r/c/p:set-axis  Esc:back",
+            AppMode::TileSelect { .. } => "hl:select  Enter:cycle  r/c/p/n:set-axis  Esc:back",
             AppMode::CommandMode { .. } => ":q quit  :w save  :import  :add-cat  :formula  :show-item  :help",
             AppMode::ImportWizard => "Space:toggle  c:cycle  Enter:next  Esc:cancel",
             _ => "",

src/ui/category_panel.rs

@@ -14,6 +14,7 @@ fn axis_display(axis: Axis) -> (&'static str, Color) {
         Axis::Row => ("Row ↕", Color::Green),
         Axis::Column => ("Col ↔", Color::Blue),
         Axis::Page => ("Page ☰", Color::Magenta),
+        Axis::None => ("None ∅", Color::DarkGray),
     }
 }
 

src/ui/grid.rs

@@ -291,7 +291,7 @@ impl<'a> GridWidget<'a> {
                                 continue;
                             }
                         };
-                        let value = self.model.evaluate(&key);
+                        let value = self.model.evaluate_aggregated(&key, &layout.none_cats);
 
                         let cell_str = format_value(value.as_ref(), fmt_comma, fmt_decimals);
                         let is_selected = ri == sel_row && ci == sel_col;
@@ -378,7 +378,7 @@ impl<'a> GridWidget<'a> {
                     }
                     let total: f64 = (0..layout.row_count())
                         .filter_map(|ri| layout.cell_key(ri, ci))
-                        .map(|key| self.model.evaluate_f64(&key))
+                        .map(|key| self.model.evaluate_aggregated_f64(&key, &layout.none_cats))
                         .sum();
                     let total_str = format_f64(total, fmt_comma, fmt_decimals);
                     buf.set_string(

src/ui/tile_bar.rs

@@ -14,6 +14,7 @@ fn axis_display(axis: Axis) -> (&'static str, Color) {
         Axis::Row => ("↕", Color::Green),
         Axis::Column => ("↔", Color::Blue),
         Axis::Page => ("☰", Color::Magenta),
+        Axis::None => ("∅", Color::DarkGray),
     }
 }