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 <[email protected]>

src/app/dimension_preview_tests.rs

@@ -63,7 +63,9 @@ fn ordinate_preview_matches_commit() {
     assert!(app.dimension_preview_entities(i, DVec3::ZERO).is_none());
     let _ = app.feed_command(StepInput::Point(DVec3::new(12.5, 40.0, 0.0)));
     let entity = commit_and_compare(&mut app, i, DVec3::new(12.5, 90.0, 0.0));
-    assert_eq!(text(&app, &entity), "12.5");
+    // A new drawing is metric and current on ISO-25, whose decimal separator
+    // is a comma and whose trailing zeros are suppressed.
+    assert_eq!(text(&app, &entity), "12,5");
 }
 
 #[test]