fix: respect repeat uniform in POM silhouette discard

[dswhy]

Hey there! Found a little bug when testing this awesome material :)

createPomMaterial({ repeat: N }) with N > 1 renders only the [0, 1] × [0, 1] corner of the surface. At repeat: 4 you see ~1/16 of the geometry; the rest is discarded.

Cause

The UV is scaled by repeat before marching, so the ray-marcher works in [0, repeat] space — but the silhouette discard still tests against the literal [0, 1]:

const scaledUv = uv().mul(repeatUniform);  // ∈ [0, repeat]
// ...inside parallaxOcclusionMapping:
currentPos.x.greaterThan(1).or(...).discard();  // wrong upper bound

Bounds and coordinate space disagree, so everything past the first tile gets killed.

Fix

Thread repeatUniform into parallaxOcclusionMapping and use it as the discard upper bound. Three-line change, no extra recompile when the slider moves (already a uniform).

Verified

• repeat: 1 — pixel-identical to current behavior
• repeat > 1 — full surface tiles, silhouette still clips at the geometry edge
• POM-disabled path untouched

I verified locally since it didn't really make sense to modify the current example. But happy to set something up if you want.

Best!