feat(dynamic-input): ARC specs + ellipse-arc preview fixes

- ARC: per-step DynSpec for the typed-value modes — included-angle (SCA,
  CSA), chord length (SCL, CSL) and radius (SER) show their box and route
  the typed value through on_text_input via a new dyn_commit_as_text()
  hook; the angle box previews the live span. Point/3P/SCE steps stay on
  the legacy polar path.
- ARC + ellipse-arc: derive the previewed sweep direction from the swept
  angle with a ~10° tolerance and advance the reference only on a clear
  move, so small cursor jitter no longer flips the arc. Ellipse uses the
  parametric angle so a flat ellipse isn't sticky.
- Ellipse arc: the start-angle step now shows a line from the centre to
  the cursor (it only picks the start angle) instead of a misleading arc.
- Ellipse arc: use the same minor-axis direction (Z x major) as the
  rendered entity so the committed arc matches the preview instead of
  mirroring across the major axis.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/view.rs

@@ -736,6 +736,11 @@ impl OpenCADStudio {
                     .map(|(idx, f)| {
                         let value = match (&f.buffer, live) {
                             (Some(b), _) => b.clone(),
+                            // An angle step with a command-supplied live value
+                            // (ARC span / direction) shows it in degrees.
+                            (None, Some(lv)) if f.component == DynComponent::Angle => {
+                                format!("{lv:.1}")
+                            }
                             (None, Some(lv))
                                 if matches!(
                                     f.component,