feat(web): tint objects by their ColorDiffuse

Model ColorDiffuse in shared types and multiply each viewer's material color by the per-object tint, including textured faces and loaded custom models.

apps/web/src/components/viewers/sharedResources.ts

@@ -1,4 +1,25 @@
 import * as THREE from 'three';
+import type { TTSObject } from '@tts/shared';
+
+/**
+ * The per-object tint (`ColorDiffuse`, 0–1 per channel) as a three.js color,
+ * defaulting to white when absent. TTS multiplies this by the object's base
+ * color, so textured faces are tinted too.
+ */
+export function objectTint(object: TTSObject): THREE.Color {
+  const c = object.ColorDiffuse;
+  return c ? new THREE.Color(c.r, c.g, c.b) : new THREE.Color(1, 1, 1);
+}
+
+/** A stable cache key fragment for a tint, so tinted variants don't collide. */
+export function tintKey(color: THREE.Color): string {
+  return `${color.r},${color.g},${color.b}`;
+}
+
+/** Multiply a base color by the object's tint. */
+export function tintedColor(base: THREE.Color, tint: THREE.Color): THREE.Color {
+  return base.clone().multiply(tint);
+}
 
 /**
  * Module-level caches so the full-setup view can share geometry and materials