Fix #847: draw Underline and Strikethrough

The styles were stored on the text and written to SVG's text-decoration,
but the type was drawn without the lines. vectorcraft_text::decorations
now gives each underlined or struck-through stretch of a run on a line
its bar, placed and sized from the font's own underline and strikeout
metrics (with fallbacks for fonts that have none). The canvas, Create
Outlines, PDF export (outlined and real text) and SVG's outlined text
draw them in the run's paint.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/typecmd.rs

@@ -251,6 +251,13 @@ fn create_outlines(s: &mut Session, _: &Value) -> Result<Value> {
                 node.appearance = st.appearance();
                 children.push(Arc::new(node));
             }
+            // Underline and strikethrough bars become paths of their run's paint too (#847).
+            for (run, bar) in vectorcraft_text::decorations(&lay, vectorcraft_text::FontDb::global(), &t) {
+                let st = t.runs.get(run).map(|r| r.style.clone()).unwrap_or_else(|| t.first_style());
+                let mut node = shape_node(d, PathData::from_bezpath(&bar).transformed(t.xf), None);
+                node.appearance = st.appearance();
+                children.push(Arc::new(node));
+            }
             let (par, idx, _) = d.position(tid).ok_or(EngineError::NoNode(tid))?;
             d.remove(tid)?;
             if children.is_empty() {