M7.4: model import

New crate effectcraft-model (L2): glTF 2.0 (.gltf/.glb, data URIs, external buffers and
images, PBR metallic-roughness with base/MR/normal/occlusion/emissive textures, node
hierarchy, skins, step/linear/cubic animations) and OBJ/MTL import, parametric primitives,
extruded/bevelled outline meshes and polygon triangulation with holes.

Project: FootageKind::Model, LayerSource::Model/Primitive, Layer::environment, Geometry and
Material Options builders, Environment light Source. Media probes and loads models
(FootageSource::model). Engine: layer.newModel, layer.new3dPrimitive/newPrimitive,
comp.renderer, layer.environment, material.set/reset/duplicateAssign/revealSource (stubs
replaced); File > Import and layer.addItem pick up models. Hand-written fixtures with
attribution sidecars.

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

docs/architecture.md

@@ -22,6 +22,7 @@ cpal or muda. Everything in L0 to L4, the egui UI and the web app also build for
 | L2 | `project` | The document: items, compositions, layers, the property tree, render queue model, `.ecproj` serde |
 | L2 | `text` | Fonts, shaping, layout, per-glyph geometry, text animators and selectors |
 | L2 | `effects` | The effect registry (241 effects) and their CPU implementations |
+| L2 | `model` | 3D models for Advanced 3D: glTF 2.0 (`.gltf`/`.glb`) and OBJ/MTL import (meshes, PBR metallic-roughness materials and textures, node hierarchy, skins, animations), parametric primitives, extruded/bevelled outline meshes and polygon triangulation |
 | L2 | `track` | Motion tracking: feature/search region point tracking (pyramid normalized cross-correlation, Lucas–Kanade sub-pixel refinement), confidence, homography/affine/similarity solves |
 | L3 | `render` | Evaluation and compositing: sources, masks, effects, transforms, 3D, motion blur, mattes, blending, layer cache, audio mixdown |
 | L3 | `media` | Footage decoding (FilmCraft's pure-Rust codecs), image sequences, frame cache |