fix(3d): revolve axis and OBJ import use the Z-up world, not stale Y-up

The truck B-rep pipeline is Z-up (solids extrude/raise along Z, profile
wires convert pass-through), but two spots still assumed a Y-up world:
- REVOLVE swapped the axis/origin to (x, z, y), so the revolve axis sat
  in the XZ plane while the profile sat in XY → wrong solid. Use the
  axis/origin straight through.
- OBJ import kept Y-up coordinates as-is on the (now Z-up) viewport, so
  imported meshes lay on their side. Rotate +90° about X on import
  (positions + normals): (x, y, z) → (x, -z, y).

EXTRUDE (sweep along +Z) and the box/cylinder primitives were already
Z-up and unchanged.

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

src/app/cmd_result.rs

@@ -1230,11 +1230,11 @@ impl OpenCADStudio {
                         let wire = wire?;
                         let origin = Point3::new(
                             axis_start.x as f64,
-                            axis_start.z as f64,
                             axis_start.y as f64,
+                            axis_start.z as f64,
                         );
                         let dir = (axis_end - axis_start).normalize();
-                        let axis = TruckVec3::new(dir.x as f64, dir.z as f64, dir.y as f64);
+                        let axis = TruckVec3::new(dir.x as f64, dir.y as f64, dir.z as f64);
                         let shell = builder::rsweep(
                             &wire,
                             origin,

src/io/obj.rs

@@ -27,14 +27,15 @@ pub fn parse_obj(src: &str, color: [f32; 4]) -> Option<MeshModel> {
             "v" => {
                 let vals: Vec<f32> = parts.filter_map(|s| s.parse().ok()).collect();
                 if vals.len() >= 3 {
-                    // OBJ: Y-up right-handed.  OpenCADStudio viewport is also Y-up → keep as-is.
-                    positions.push([vals[0], vals[1], vals[2]]);
+                    // OBJ is Y-up right-handed; OpenCADStudio's world is Z-up.
+                    // Rotate +90° about X so OBJ Y→world Z (up): (x, y, z) → (x, -z, y).
+                    positions.push([vals[0], -vals[2], vals[1]]);
                 }
             }
             "vn" => {
                 let vals: Vec<f32> = parts.filter_map(|s| s.parse().ok()).collect();
                 if vals.len() >= 3 {
-                    normals_raw.push([vals[0], vals[1], vals[2]]);
+                    normals_raw.push([vals[0], -vals[2], vals[1]]);
                 }
             }
             "f" => {