ACAD_SURFACE entities now load and render. Their NURBS faces are
tessellated by building a truck BSplineSurface from the ACIS `spline-surface`
control net and knot vectors, then sampling its parametric grid — reusing the
same NURBS kernel the Model tab already builds on. Analytic faces
(plane/cone/sphere/torus) continue through the existing tessellator.
- New spline_tess.rs: parse the ACIS `nubs` block (degrees, knots with the
clamped end-multiplicity fix, control grid) into a truck BSplineSurface and
mesh it.
- tessellate_surface + Surface wired through the mesh-build, fallback-wire,
and entity-classification paths.
- Bump acadrust to the commit that adds the Surface entity.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
