Prove the render path end-to-end: bring up UIKit + Metal (already
scaffolded), clear to a solid blue, and draw one centered orange quad via
the GPU protocol's clear+quad path — an MSL pass-through pipeline plus a
6-vertex (2-triangle) NDC buffer, created lazily once the MTLDevice exists.
Geometry is NDC [-0.5, 0.5]² so the quad is the central 50%x50% of the
drawable regardless of device resolution, keeping the screenshot golden
unambiguous. Background (0.10, 0.20, 0.55), quad (1.0, 0.6, 0.0).
goldens/p0_quad.png is the first screenshot golden, captured from the
booted iOS 26.0 simulator after install + launch.
df6cb2161d
