[Lemiort]

Closes #28.

Problem

Normals were transformed by rotation only, while vertex positions used rotation plus nonuniform scale. This makes the resulting normals non-perpendicular to the transformed surface and produces incorrect diffuse/specular lighting.

Summary

• compute the inverse-scale/rotation normal matrix for each transform
• upload the normal matrix for both individual and instanced mesh draws
• use it in both forward and deferred geometry vertex shaders
• use a finite rotation-only fallback for collapsed (near-zero scale) geometry
• add regression tests proving transformed normals remain perpendicular and singular scales remain finite

Verification

• cmake --build build/build/Release --target NEE math_migration_tests opengl_render_tests
• ctest --test-dir build/build/Release -R "ObjectTransform|OpenGLRender" --output-on-failure (14/14 passed)
• ctest --test-dir build/build/Release --output-on-failure --no-tests=error (36/36 passed)