Metric new drawings with the ISO-25 dimension style current

A new drawing is metric (measurement 1, millimetre insertion units) and
carries the reference's ISO-25 dimension style as its current style, so
dimensions and annotational constraints draw at readable metric sizes
instead of Standard's imperial 0.18 text.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/scene/entity.rs

@@ -2728,6 +2728,13 @@ impl Scene {
     /// standard linetypes and a compatible page setup on every paper layout.
     pub fn populate_new_drawing_defaults(&mut self) {
         crate::io::linetypes::populate_document(&mut self.document);
+        // A new drawing is metric, as the reference's ISO template: millimetre
+        // insertion units, metric measurement, and the ISO-25 dimension style
+        // current. Standard stays available for imperial work.
+        self.document.header.measurement = 1;
+        self.document.header.insertion_units = 4;
+        crate::scene::creation_style::ensure_iso_dim_style(&mut self.document);
+        self.document.header.current_dimstyle_name = "ISO-25".to_string();
         for obj in self.document.objects.values_mut() {
             if let acadrust::objects::ObjectType::Layout(l) = obj {
                 if l.name != "Model" {