Render actual 3D geometry (cubes + ground plane) in the Viewport panel
using the existing mesh_shader.wgsl Blinn-Phong pipeline with orbit
camera controls (left-drag to orbit, middle-drag to pan, scroll to zoom).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Add UiRenderer with wgpu render pipeline for 2D UI overlay rendering.
Includes WGSL shader with orthographic projection, alpha blending,
and R8Unorm font atlas sampling. Font pixel (0,0) set to white for
solid-color rect rendering via UV (0,0).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
