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/chart/src/tests.rs

@@ -5,6 +5,8 @@ use gridcraft_model::{Anchor, Chart, ChartKind, Color, LegendPos, Series, Sparkl
 
 use crate::*;
 
+mod data_table;
+
 const ALL_KINDS: [ChartKind; 26] = [
     ChartKind::ColumnClustered,
     ChartKind::ColumnStacked,
@@ -43,6 +45,7 @@ fn chart(kind: ChartKind) -> Chart {
         series: vec![],
         legend: LegendPos::Bottom,
         data_labels: true,
+        data_table: None,
         gridlines: true,
         style: 0,
         x_title: Some("Quarter".into()),