M7: add data tables beneath charts

Add command and UI controls for chart data tables, shared chart and PDF rendering, and native XLSX persistence. Cover live values, blanks, formatting, alignment, undo/redo, bounds and table flags with regression tests.

Co-Authored-By: Codex <noreply@openai.com>

crates/engine/src/cmd/insert/chart.rs

@@ -260,6 +260,7 @@ pub fn build_chart(s: &Session, p: &Json) -> Result<(usize, Chart)> {
         series,
         legend: if matches!(kind, ChartKind::Pie | ChartKind::Doughnut) { LegendPos::Right } else { LegendPos::Bottom },
         data_labels: false,
+        data_table: None,
         gridlines: !matches!(kind, ChartKind::Pie | ChartKind::Doughnut | ChartKind::Treemap | ChartKind::Sunburst | ChartKind::Funnel),
         style: 1,
         x_title: None,