feat(render): draw ACIS solids as B-rep feature edges, meshes as tri edges

Solid wireframes rendered every triangle edge of the tessellation, so a
curved solid read as a dense mesh instead of its real outline. Now each ACIS
solid's B-rep face-boundary edges are collected from the SAT `edge` records
(straight edges as segments, ellipse/circle edges sampled along their bounded
arc), body-transformed and split into the double-single pair, and stored on
the MeshLodSet. The block-instance and top-level offset paths transform these
edges alongside the mesh vertices.

The batch builder routes a solid with feature edges into a dedicated LineList
vertex buffer and skips its triangle wireframe; a mesh with no B-rep edges
keeps its triangulation edges. Edge colour follows the display mode: the flat
`fs_edge` shader draws the entity colour in the lines-only modes (wireframe,
hidden-line) and a `fs_edge_black` twin forces black for the edge overlay in
filled render modes.

Verified: the Clinic storefront arch bars now yield ~14-16 clean edge
segments (vs the full triangulation) bounded to the solid's true extent.

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

src/shaders/mesh.wgsl

@@ -79,3 +79,17 @@ fn fs_main(in: VertexOut) -> @location(0) vec4<f32> {
     let rgb = in.color.rgb * clamp(diff, 0.0, 1.0);
     return vec4<f32>(rgb, in.color.a);
 }
+
+// Edge fragment (LineList): flat entity colour, no lighting. Used for the
+// wireframe and hidden-line edge passes so lines read at their true colour.
+@fragment
+fn fs_edge(in: VertexOut) -> @location(0) vec4<f32> {
+    return vec4<f32>(in.color.rgb, 1.0);
+}
+
+// Edge fragment for filled render modes: force black so edges frame the shaded
+// fill regardless of the solid's colour.
+@fragment
+fn fs_edge_black(in: VertexOut) -> @location(0) vec4<f32> {
+    return vec4<f32>(0.0, 0.0, 0.0, 1.0);
+}