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/ui/effect.rs

@@ -90,6 +90,68 @@ impl Effect for RemoveFormula {
     }
 }
 
+/// Re-enter edit mode by reading the cell value at the current cursor.
+/// Used after commit+advance to continue data entry.
+#[derive(Debug)]
+pub struct EnterEditAtCursor;
+impl Effect for EnterEditAtCursor {
+    fn apply(&self, app: &mut App) {
+        let ctx = app.cmd_context(crossterm::event::KeyCode::Null, crossterm::event::KeyModifiers::NONE);
+        let value = if let Some(v) = &ctx.records_value {
+            v.clone()
+        } else {
+            ctx.cell_key
+                .as_ref()
+                .and_then(|k| ctx.model.get_cell(k).cloned())
+                .map(|v| v.to_string())
+                .unwrap_or_default()
+        };
+        drop(ctx);
+        app.buffers.insert("edit".to_string(), value);
+        app.mode = AppMode::Editing {
+            buffer: String::new(),
+        };
+    }
+}
+
+#[derive(Debug)]
+pub struct TogglePruneEmpty;
+impl Effect for TogglePruneEmpty {
+    fn apply(&self, app: &mut App) {
+        let v = app.model.active_view_mut();
+        v.prune_empty = !v.prune_empty;
+    }
+}
+
+#[derive(Debug)]
+pub struct ToggleCatExpand(pub String);
+impl Effect for ToggleCatExpand {
+    fn apply(&self, app: &mut App) {
+        if !app.expanded_cats.remove(&self.0) {
+            app.expanded_cats.insert(self.0.clone());
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct RemoveItem {
+    pub category: String,
+    pub item: String,
+}
+impl Effect for RemoveItem {
+    fn apply(&self, app: &mut App) {
+        app.model.remove_item(&self.category, &self.item);
+    }
+}
+
+#[derive(Debug)]
+pub struct RemoveCategory(pub String);
+impl Effect for RemoveCategory {
+    fn apply(&self, app: &mut App) {
+        app.model.remove_category(&self.0);
+    }
+}
+
 // ── View mutations ───────────────────────────────────────────────────────────
 
 #[derive(Debug)]