T14c Tables: DataGrid, Spreadsheet with formulas, merges, frozen panes and fill, TreeTable, PivotTable

tasks/ch11-20.md

@@ -144,10 +144,10 @@
 
 ## T14c Tables · Grids
 
-- [ ] DataGrid
-- [ ] Spreadsheet — formula subset, merge, freeze, fill handle
-- [ ] TreeTable
-- [ ] PivotTable
+- [x] DataGrid → `tables::DataGrid`
+- [x] Spreadsheet — formula subset, merge, freeze, fill handle → `tables::Spreadsheet`; SUM, AVERAGE, MIN, MAX, COUNT over ranges
+- [x] TreeTable → `tables::TreeTable`, `TreeRow`
+- [x] PivotTable → `tables::PivotTable`
 
 ## T15 Charts — `src/charts`