M7.5: advanced 3D renderer

Advanced 3D comps render their 3D runs as one scene of world-space triangles: model and
primitive layers (meshes, skinning, animation clips by layer time), extruded text/shape
layers, and textured cards for every other layer with their Material Options. Shading is
physically based in linear light: Cook-Torrance GGX + Lambert for parallel/spot/point lights
(AE falloff and cone), ambient lights, image-based light from an Environment light's layer
(equirectangular; cosine irradiance map + roughness mip chain + split-sum BRDF fit), and
PCF shadow maps (spot/parallel/point cube faces). 2x2 SSAA, depth of field as a gather blur
by circle of confusion, back to the working encoding.

The software rasteriser (depth buffer, top-left rule, perspective-correct, opaque visibility
then sorted transparent blending) is the reference and CI path; effectcraft-gpu implements
Accelerator::raster_3d with a wgpu render pipeline (advanced3d.wgsl) and matches it within
tolerance. Environment layers are hidden from both renderers.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/commands/model3d.rs

@@ -349,7 +349,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "3D Model Layer",
             [],
             None,
-            "{item?: id|name (a 3D model footage item) | path?: .gltf|.glb|.obj file, name?, time? (s)}",
+            "{item?: id or name of a 3D model footage item, path?: a .gltf, .glb or .obj file to import, name?, time? (s)}",
             has_comp,
             new_model
         ),