Resolves #8484

Changes:

This PR adds visual regression tests for WebGL 3D primitives that were not previously covered:

• cylinder()
• cone()
• ellipsoid()
• torus()

Each test renders a single primitive using a small, deterministic scene with stable lighting.
The goal is to catch visual regressions in geometry or lighting during future refactors.
No APIs or rendering behavior are changed, this is an additive test-only update.

Screenshots of the change:

Baseline screenshots for each primitive were generated and added under:
test/unit/visual/screenshots/WebGL/3D Primitives/

PR Checklist

• npm run lint passes
• Inline reference is included / updated (not applicable)
• Unit tests are included / updated