fix: review fixes for the metric template and the radial constraint

A new drawing (#1441) recorded ISO-25 as the current dimension style by
name only. Every other place that changes it sets the header's handle as
well, and a DWG carries the current style by handle alone, so a saved new
drawing reopened on Standard. The style's handle now comes back from the
helper that adds it.

A radius constraint (#1443) anchored the circle's centre from the shape of
its references — one whole entity — but a single whole reference is also a
line's length, whose start is what stays. The entity decides now.

The two tests that encoded the replaced rules follow them: a negative
radius validates by its magnitude, as a negative distance already did, and
only zero is refused; a new drawing's dimension text reads at ISO-25's
comma separator.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/scene/creation_style.rs

@@ -36,14 +36,16 @@ fn named_text_style(doc: &CadDocument, name: &str) -> Option<TextStyle> {
 }
 
 /// 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
+/// metric template) when the drawing has none of that name, and hands back its
+/// handle: the header records the current dimension style by handle as well as
+/// by name, and a DWG carries only the handle.
+pub fn ensure_iso_dim_style(doc: &mut CadDocument) -> Handle {
+    if let Some(style) = doc
         .dim_styles
         .iter()
-        .any(|style| style.name.eq_ignore_ascii_case("ISO-25"))
+        .find(|style| style.name.eq_ignore_ascii_case("ISO-25"))
     {
-        return;
+        return style.handle;
     }
     let mut style = DimStyle::new("ISO-25");
     style.handle = doc.allocate_handle();
@@ -82,7 +84,9 @@ pub fn ensure_iso_dim_style(doc: &mut CadDocument) {
     style.dimjogang = std::f64::consts::FRAC_PI_2;
     style.dimmzf = 100.0;
     style.dimaltmzf = 100.0;
+    let handle = style.handle;
     let _ = doc.dim_styles.add(style);
+    handle
 }
 
 fn named_dim_style(doc: &CadDocument, name: &str) -> Option<DimStyle> {