feat: add new commands for records mode and category management

Add new commands for enhanced data entry and category management.

AddRecordRow: Adds a new record row in records mode with empty value.
TogglePruneEmpty: Toggles pruning of empty rows/columns in pivot mode.
ToggleRecordsMode: Switches between records and pivot layout.
DeleteCategoryAtCursor: Removes a category and all its cells.
ToggleCatExpand: Expands/collapses a category in the tree.
FilterToItem: Filters to show only items matching cursor position.

Model gains remove_category() and remove_item() to delete categories
and items along with all referencing cells and formulas.

Co-Authored-By: fiddlerwoaroof/git-smart-commit (unsloth/Qwen3.5-35B-A3B-GGUF:Q5_K_M)

src/model/types.rs

@@ -107,6 +107,47 @@ impl Model {
         Ok(id)
     }
 
+    /// Remove a category and all cells that reference it.
+    pub fn remove_category(&mut self, name: &str) {
+        if !self.categories.contains_key(name) {
+            return;
+        }
+        self.categories.shift_remove(name);
+        // Remove from all views
+        for view in self.views.values_mut() {
+            view.on_category_removed(name);
+        }
+        // Remove cells that have a coord in this category
+        let to_remove: Vec<CellKey> = self
+            .data
+            .iter_cells()
+            .filter(|(k, _)| k.get(name).is_some())
+            .map(|(k, _)| k)
+            .collect();
+        for k in to_remove {
+            self.data.remove(&k);
+        }
+        // Remove formulas targeting this category
+        self.formulas
+            .retain(|f| f.target_category != name);
+    }
+
+    /// Remove an item from a category and all cells that reference it.
+    pub fn remove_item(&mut self, cat_name: &str, item_name: &str) {
+        if let Some(cat) = self.categories.get_mut(cat_name) {
+            cat.remove_item(item_name);
+        }
+        let to_remove: Vec<CellKey> = self
+            .data
+            .iter_cells()
+            .filter(|(k, _)| k.get(cat_name) == Some(item_name))
+            .map(|(k, _)| k)
+            .collect();
+        for k in to_remove {
+            self.data.remove(&k);
+        }
+    }
+
     pub fn category_mut(&mut self, name: &str) -> Option<&mut Category> {
         self.categories.get_mut(name)
     }
@@ -527,6 +568,31 @@ mod model_tests {
         assert_eq!(m.get_cell(&k4), Some(&CellValue::Number(40.0)));
     }
 
+    #[test]
+    fn remove_category_deletes_category_and_cells() {
+        let mut m = Model::new("Test");
+        m.add_category("Region").unwrap();
+        m.add_category("Product").unwrap();
+        m.category_mut("Region").unwrap().add_item("East");
+        m.category_mut("Product").unwrap().add_item("Shirts");
+        m.set_cell(
+            coord(&[("Region", "East"), ("Product", "Shirts")]),
+            CellValue::Number(42.0),
+        );
+        m.remove_category("Region");
+        assert!(m.category("Region").is_none());
+        // Cells referencing Region should be gone
+        assert_eq!(
+            m.data.iter_cells().count(),
+            0,
+            "all cells with Region coord should be removed"
+        );
+        // Views should no longer know about Region
+        // (axis_of would panic for unknown category, so check categories_on)
+        let v = m.active_view();
+        assert!(v.categories_on(crate::view::Axis::Row).is_empty());
+    }
+
     #[test]
     fn create_view_copies_category_structure() {
         let mut m = Model::new("Test");