#729: import STL 3D models (binary and ASCII)

Problem: After Effects 26 imports STL models besides glTF and OBJ; we
refused .stl files, and the Media Browser and import dialog did not list
them as models.

Fix: a pure-Rust STL reader in effectcraft-model (binary and ASCII,
detected from the contents; several ASCII solids and polygon loops;
VisCAM/SolidView and Materialise Magics facet colours as plain
materials; Z-up turned to the model's Y-up; faceted normals from the
winding). Truncated, empty or non-finite input is an error, never a
crash. .stl is now a model extension for import, probing, the Media
Browser, the import dialog and the system report.

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

crates/engine/src/commands/app_more.rs

@@ -316,6 +316,7 @@ pub const IMPORT_FORMATS: &[&str] = &[
     "Opus",
     "glTF/GLB",
     "OBJ",
+    "STL",
     "Lottie JSON",
 ];
 

crates/engine/src/commands/model3d.rs

@@ -1,4 +1,4 @@
-//! Advanced 3D: model layers (File ▸ Import of glTF/OBJ, Layer ▸ New ▸ 3D primitives), the
+//! Advanced 3D: model layers (File ▸ Import of glTF/OBJ/STL, Layer ▸ New ▸ 3D primitives), the
 //! comp renderer switch, Layer ▸ Environment Layer, Geometry Options for extruded text and
 //! shapes, and Layer ▸ Material commands.
 
@@ -376,7 +376,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "3D Model Layer",
             [],
             None,
-            "{item?: id or name of a 3D model footage item, path?: a .gltf, .glb or .obj file to import, name?, time? (s), index? (1-based stack position), position? ([x, y] comp px)}; switches a Classic 3D comp to Advanced 3D",
+            "{item?: id or name of a 3D model footage item, path?: a .gltf, .glb, .obj or .stl file to import, name?, time? (s), index? (1-based stack position), position? ([x, y] comp px)}; switches a Classic 3D comp to Advanced 3D",
             has_comp,
             new_model
         ),

crates/engine/src/media_browser.rs

@@ -197,7 +197,7 @@ const VIDEO: &[&str] = &["mp4", "m4v", "mov", "webm", "mkv", "avi", "mxf", "gif"
 const IMAGE: &[&str] = &["png", "jpg", "jpeg", "tif", "tiff", "exr", "bmp", "webp", "psd", "psb", "svg", "tga", "dpx", "hdr"];
 const AUDIO: &[&str] = &["wav", "aif", "aiff", "mp3", "m4a", "aac", "flac", "ogg", "opus"];
 const DATA: &[&str] = &["json", "csv", "tsv", "mgjson"];
-const MODEL: &[&str] = &["gltf", "glb", "obj"];
+const MODEL: &[&str] = &["gltf", "glb", "obj", "stl"];
 
 /// Kind of file from its extension.
 pub fn kind_of(path: &str) -> Option<&'static str> {