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/creation_style.rs

@@ -35,6 +35,56 @@ fn named_text_style(doc: &CadDocument, name: &str) -> Option<TextStyle> {
         .cloned()
 }
 
+/// Adds the reference's ISO-25 dimension style (the current style of its
+/// metric template) when the drawing has none of that name.
+pub fn ensure_iso_dim_style(doc: &mut CadDocument) {
+    if doc
+        .dim_styles
+        .iter()
+        .any(|style| style.name.eq_ignore_ascii_case("ISO-25"))
+    {
+        return;
+    }
+    let mut style = DimStyle::new("ISO-25");
+    style.handle = doc.allocate_handle();
+    style.dimtxt = 2.5;
+    style.dimasz = 2.5;
+    style.dimcen = 2.5;
+    style.dimexe = 1.25;
+    style.dimexo = 0.625;
+    style.dimgap = 0.625;
+    style.dimdli = 3.75;
+    style.dimtad = 1;
+    style.dimtih = false;
+    style.dimtoh = false;
+    style.dimtofl = true;
+    style.dimtix = false;
+    style.dimsoxd = false;
+    style.dimdsep = i16::from(b',');
+    style.dimlunit = 2;
+    style.dimdec = 2;
+    style.dimtdec = 2;
+    style.dimaunit = 0;
+    style.dimadec = 0;
+    style.dimazin = 0;
+    style.dimzin = 8;
+    style.dimtzin = 8;
+    style.dimatfit = 3;
+    style.dimtmove = 0;
+    style.dimscale = 1.0;
+    style.dimlfac = 1.0;
+    style.dimtfac = 1.0;
+    style.dimaltf = 0.03937007874016;
+    style.dimaltd = 3;
+    style.dimalttd = 3;
+    style.dimaltu = 2;
+    style.dimfxl = 1.0;
+    style.dimjogang = std::f64::consts::FRAC_PI_2;
+    style.dimmzf = 100.0;
+    style.dimaltmzf = 100.0;
+    let _ = doc.dim_styles.add(style);
+}
+
 fn named_dim_style(doc: &CadDocument, name: &str) -> Option<DimStyle> {
     doc.dim_styles
         .iter()

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" {