Extend sketch constraints toward FreeCAD parity, staying DWG-native-compatible

Arcs are now full constraint participants (center/radius via the existing
Circle-shaped solver path, plus real endpoints kept consistent by arc-rules
CurveValue constraints); adds Diameter/DistanceX/DistanceY/ArcLength/Normal
constraint kinds and initial Ellipse entity support (center-based
constraints only). DWG-native class mappings and gaps (ArcLength, Ellipse)
are grounded against real ObjectARX headers rather than guessed, so files
saved with DWG-native constraints stay honest about what AutoCAD can
actually represent.

Also fixes a case-sensitivity bug where a lowercase named-parameter
reference typed at a dimensional constraint's value prompt was rejected
(the command line uppercases SingleToken input before the parameter-name
lookup), and adds a "Used by" column to the Named Parameters panel.

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

src/app/view/modal.rs

@@ -175,13 +175,15 @@ impl OpenCADStudio {
                 )
             }
             super::super::ModalKind::NamedParameters => {
+                let scene = &self.tabs[self.active_tab].scene;
                 sized_flow(
                     ex,
-                    620,
+                    820,
                     520,
                     |flow| {
                         crate::ui::window::named_parameters::view_window(
                             &self.named_parameter_editor_rows,
+                            scene,
                             flow,
                         )
                     },