feat: complex linetype text elements and ellipse quadrant snaps

Complex linetypes now render embedded text elements (e.g. GAS_LINE's
"GAS" labels): the LtSegment::Text variant is parsed from LIN files,
scaled along with shape/dash segments, and tessellated via
cxf::tessellate_text_ex aligned to the linetype direction.

Full ellipses gain four Quadrant snap hints at ±major/±minor axis
endpoints in addition to the existing Center snap, matching AutoCAD
snap behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/entities/ellipse.rs

@@ -71,9 +71,24 @@ fn to_truck(ell: &Ellipse) -> TruckEntity {
         let edge_upper = Edge::new(&v_pos, &v_neg, Curve::BSplineCurve(spl_u));
         let edge_lower = Edge::new(&v_neg, &v_pos, Curve::BSplineCurve(spl_l));
         let wire: Wire = [edge_upper, edge_lower].into_iter().collect();
+        // Quadrant points at ±major and ±minor axis endpoints.
+        let q = |lx: f64, lz: f64| {
+            Vec3::new(
+                (cx + lx * u.x as f64 + lz * v_axis.x as f64) as f32,
+                (cy + lx * u.y as f64 + lz * v_axis.y as f64) as f32,
+                cz as f32,
+            )
+        };
+        let snap_pts = vec![
+            (center_v3, SnapHint::Center),
+            (q(r_major, 0.0),  SnapHint::Quadrant),
+            (q(-r_major, 0.0), SnapHint::Quadrant),
+            (q(0.0, r_minor),  SnapHint::Quadrant),
+            (q(0.0, -r_minor), SnapHint::Quadrant),
+        ];
         TruckEntity {
             object: TruckObject::Contour(wire),
-            snap_pts: vec![(center_v3, SnapHint::Center)],
+            snap_pts,
             tangent_geoms: vec![],
             key_vertices: vec![],
         }

src/entities/mod.rs

@@ -22,7 +22,7 @@ pub mod shape;
 pub mod solid;
 pub mod spline;
 pub mod text;
-mod text_support;
+pub(crate) mod text_support;
 pub mod table;
 pub mod tolerance;
 pub mod traits;