feat(tests): Add test_mesh tool for OBJ loading and normal visualization

Implemented a new standalone test tool 'test_mesh' to:
- Load a .obj file specified via command line.
- Display the mesh with rotation and basic lighting on a tiled floor.
- Provide a '--debug' option to visualize vertex normals as cyan lines.
- Updated asset_packer to auto-generate smooth normals for OBJs if missing.
- Fixed various WGPU API usage inconsistencies and build issues on macOS.
- Exposed Renderer3D::GetVisualDebug() for test access.
- Added custom Vec3 struct and math utilities for OBJ parsing.
This tool helps verify mesh ingestion and normal computation independently of the main demo logic.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/3d/renderer.h b/src/3d/renderer.h
index 5caf19b..5c9fd38 100644
--- a/src/3d/renderer.h
+++ b/src/3d/renderer.h
@@ -65,13 +65,23 @@ class Renderer3D {
   // Set whether to use BVH acceleration
   void SetBvhEnabled(bool enabled) { bvh_enabled_ = enabled; }
 
- private:
   struct MeshGpuData {
     WGPUBuffer vertex_buffer;
     WGPUBuffer index_buffer;
     uint32_t num_indices;
   };
 
+  // HACK for test_mesh tool
+  void override_mesh_buffers(const MeshGpuData* data) {
+    temp_mesh_override_ = data;
+  }
+
+#if !defined(STRIP_ALL)
+  VisualDebug& GetVisualDebug() { return visual_debug_; }
+#endif
+
+ private:
+
   void create_pipeline();
   WGPURenderPipeline create_pipeline_impl(bool use_bvh);
   void create_mesh_pipeline();
@@ -98,6 +108,7 @@ class Renderer3D {
   bool bvh_enabled_ = true;
 
   std::map<AssetId, MeshGpuData> mesh_cache_;
+  const MeshGpuData* temp_mesh_override_ = nullptr; // HACK for test_mesh tool
 
   WGPUTextureView noise_texture_view_ = nullptr;
   WGPUTextureView sky_texture_view_ = nullptr;