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/command/keymap.rs

@@ -354,9 +354,14 @@ impl KeymapSet {
         normal.bind(KeyCode::Char('z'), none, "toggle-group-under-cursor");
         normal.bind(KeyCode::Char('H'), none, "hide-selected-row-item");
 
-        // Drill into aggregated cell / view history
+        // Drill into aggregated cell / view history / add row
         normal.bind(KeyCode::Char('>'), none, "drill-into-cell");
         normal.bind(KeyCode::Char('<'), none, "view-back");
+        normal.bind(KeyCode::Char('o'), none, "add-record-row");
+
+        // Records mode toggle and prune toggle
+        normal.bind(KeyCode::Char('R'), none, "toggle-records-mode");
+        normal.bind(KeyCode::Char('P'), none, "toggle-prune-empty");
 
         // Tile select
         normal.bind(KeyCode::Char('T'), none, "enter-tile-select");