feat(PBR): extract Blender PBR properties and apply in 3D viewer

Extract Base Color, Metallic, Roughness, Transmission, IOR from Blender
asset library materials via catalog_assets.py. Store in catalog JSON and
serve via /api/asset-libraries/pbr-map endpoint. Frontend viewers apply
PBR properties to Three.js MeshStandardMaterial using hex color strings
(avoiding Three.js ColorManagement sRGB/linear issues).

Key fixes:
- RLS bypass for material alias lookup in pbr-map endpoint
- pbrMap empty guard prevents premature grey fallback in viewers
- Cache-Control: no-cache on pbr-map requests to avoid stale data

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/cad/cadUtils.ts

@@ -1,4 +1,5 @@
 import type { PartMaterialEntry, PartMaterialMap } from '../../api/cad'
+import type { MaterialPBR, MaterialPBRMap } from '../../api/assetLibraries'
 
 /**
  * Normalize a GLB mesh name by stripping suffixes added by the export pipeline:
@@ -61,6 +62,44 @@ export function resolvePartMaterial(
   return bestKey ? partMaterials[bestKey] : undefined
 }
 
+// ---------------------------------------------------------------------------
+// remapToPartKeys
+// ---------------------------------------------------------------------------
+
+/**
+ * Remap a PartMaterialMap keyed by normalized OCC names to partKey slugs.
+ *
+ * When partKeyMap is available (from GLB extras), Excel-imported material keys
+ * like "GE360-HF_000_P_ASM_1" are converted to partKey slugs like
+ * "ge360_hf_000_p_asm_1" so they match what the viewer resolves each mesh to.
+ *
+ * Keys not found in partKeyMap are preserved as-is (backwards compat for old GLBs).
+ */
+export function remapToPartKeys(
+  materials: PartMaterialMap,
+  partKeyMap: Record<string, string>,
+): PartMaterialMap {
+  if (!partKeyMap || Object.keys(partKeyMap).length === 0) return materials
+  const mapKeys = Object.keys(partKeyMap)
+  const result: PartMaterialMap = {}
+  for (const [key, entry] of Object.entries(materials)) {
+    // 1. Exact match
+    if (partKeyMap[key]) { result[partKeyMap[key]] = entry; continue }
+    // 2. Prefix match: cad_part_materials may have extra _1 instance suffixes
+    //    that partKeyMap doesn't (e.g. "PART_04_1" vs partKeyMap "PART_04")
+    let matched = false
+    for (const mk of mapKeys) {
+      if (key.startsWith(mk + '_') || key === mk) {
+        result[partKeyMap[mk]] = entry
+        matched = true
+        break
+      }
+    }
+    if (!matched) result[key] = entry // preserve unmapped
+  }
+  return result
+}
+
 // ---------------------------------------------------------------------------
 // convertCadPartMaterials
 // ---------------------------------------------------------------------------
@@ -85,3 +124,51 @@ export function convertCadPartMaterials(
   }
   return result
 }
+
+// ---------------------------------------------------------------------------
+// PBR material helpers
+// ---------------------------------------------------------------------------
+
+/**
+ * Apply PBR material properties from the Blender asset library to a
+ * Three.js MeshStandardMaterial.
+ *
+ * The `mat` parameter is typed as `any` to avoid importing THREE in this
+ * utility module — callers pass `THREE.MeshStandardMaterial` instances.
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export function applyPBRToMaterial(mat: any, pbr: MaterialPBR): void {
+  if (!mat || !('color' in mat)) return
+  // Use hex string via color.set() — reliable across all Three.js versions and
+  // avoids colorSpace/gamma issues with setRGB() + ColorManagement.
+  mat.color.set(pbrColorHex(pbr))
+  mat.metalness = pbr.metallic
+  mat.roughness = pbr.roughness
+  if (pbr.transmission && pbr.transmission > 0.1) {
+    mat.transparent = true
+    mat.opacity = 1 - pbr.transmission * 0.7
+  }
+  mat.needsUpdate = true
+}
+
+/** Convert PBR base_color to hex string for UI swatches. */
+export function pbrColorHex(pbr: MaterialPBR): string {
+  const [r, g, b] = pbr.base_color
+  return '#' + [r, g, b].map(v => Math.round(v * 255).toString(16).padStart(2, '0')).join('')
+}
+
+/**
+ * Get a preview hex color for a material entry, using PBR data when available.
+ * Replaces the old hardcoded SCHAEFFLER_COLORS lookup.
+ */
+export function previewColorForEntry(
+  entry: PartMaterialEntry,
+  pbrMap?: MaterialPBRMap,
+): string {
+  if (entry.type === 'hex') return entry.value
+  if (pbrMap) {
+    const pbr = pbrMap[entry.value]
+    if (pbr) return pbrColorHex(pbr)
+  }
+  return '#888888'
+}