dimstyle: New starts from the selected style

New created a bare dimension style, whose defaults are inch-sized
(0.18 arrows and text). In a metric drawing its arrows came out too
small to see (#1675). It now starts from the selected style.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/style_ops.rs

@@ -714,7 +714,13 @@ impl OpenCADStudio {
         let i = self.active_tab;
         let name = self.unique_new_name(kind);
         let h = self.tabs[i].scene.document.allocate_handle();
-        self.insert_default_style(kind, &name, h);
+        // A new dimension style starts from the selected one: the bare
+        // defaults are inch-sized, so in a metric drawing its arrows and gaps
+        // would come out too small to see.
+        let src = self.style_selected(kind);
+        if kind != StyleKind::Dim || !self.clone_style_as(kind, &src, &name, h) {
+            self.insert_default_style(kind, &name, h);
+        }
         self.set_style_selected(kind, name.clone());
         self.load_style_bufs(kind);
         self.after_style_change(kind);