fix(solid): cone silhouette uses the base radius, not the root radius

The DISPSILH silhouette for a cone anchored its `CurvedGen::Cone.base` at
the face's h_min (the base rim) but stored `radius` as the surface's h=0
root radius. The silhouette builder treats `radius` as the radius AT
`base`, so its base line landed at the wrong radius and its top line
(`radius + span·tan_a`) overshot the apex — a visibly wrong outline in
wireframe, and wrong lines drawn over the (correct) shaded fill. Store the
radius at the base instead (`radius + h_min·tan_a`). Cylinders (tan_a=0)
and root-based cones (h_min=0) are unchanged.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/scene/convert/solid3d_tess.rs

@@ -719,7 +719,12 @@ fn collect_curved_gens(
                     axis: rot_dir(g.axis),
                     u_dir: rot_dir(g.u_dir),
                     v_dir: rot_dir(g.v_dir),
-                    radius: (g.radius * scale) as f32,
+                    // `radius` is the cone radius at `base`, which sits at h_min —
+                    // NOT at the surface's h=0 root. `cone_face_geom.radius` is the
+                    // root radius, so add the h_min offset (`radius + h_min·tan_a`)
+                    // or the silhouette's `r0 = radius` lands at the wrong radius
+                    // and its top `r1 = radius + span·tan_a` overshoots the apex.
+                    radius: ((g.radius + g.h_min * g.tan_a) * scale) as f32,
                     tan_a: g.tan_a as f32,
                     h_max: ((g.h_max - g.h_min) * scale) as f32,
                     theta_min: g.theta_min as f32,