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>

render-worker/scripts/catalog_assets.py

@@ -4,17 +4,75 @@ Usage:
     blender --background --python catalog_assets.py -- <blend_path>
 
 Outputs a single JSON line to stdout:
-    {"materials": ["Mat1", "Mat2", ...], "node_groups": ["NG1", ...]}
+    {"materials": [{"name": "Mat1", "base_color": [R,G,B], "metallic": 0.0, ...}, ...],
+     "node_groups": ["NG1", ...]}
 
 Only assets marked via Blender's asset system (asset_data is not None) are included.
+PBR properties are extracted from the Principled BSDF node of each material.
 """
 from __future__ import annotations
 
 import json
+import math
 import sys
 import traceback
 
 
+def _linear_to_srgb(v: float) -> float:
+    """Convert a single linear color channel to sRGB."""
+    if v <= 0.0031308:
+        return v * 12.92
+    return 1.055 * math.pow(v, 1.0 / 2.4) - 0.055
+
+
+def _extract_pbr(mat) -> dict:
+    """Extract PBR properties from a Blender material's Principled BSDF node.
+
+    Returns dict with: name, base_color (sRGB), metallic, roughness, transmission, ior.
+    Falls back to diffuse_color if no Principled BSDF found.
+    """
+    entry = {
+        "name": mat.name,
+        "base_color": [0.5, 0.5, 0.5],
+        "metallic": 0.0,
+        "roughness": 0.5,
+        "transmission": 0.0,
+        "ior": 1.45,
+    }
+
+    # Find Principled BSDF node
+    bsdf = None
+    if mat.use_nodes and mat.node_tree:
+        for node in mat.node_tree.nodes:
+            if node.type == "BSDF_PRINCIPLED":
+                bsdf = node
+                break
+
+    if bsdf:
+        # Base Color — convert linear → sRGB
+        bc = bsdf.inputs["Base Color"].default_value
+        entry["base_color"] = [
+            round(_linear_to_srgb(bc[0]), 4),
+            round(_linear_to_srgb(bc[1]), 4),
+            round(_linear_to_srgb(bc[2]), 4),
+        ]
+        entry["metallic"] = round(bsdf.inputs["Metallic"].default_value, 4)
+        entry["roughness"] = round(bsdf.inputs["Roughness"].default_value, 4)
+        # Transmission Weight (Blender 4.0+) or Transmission (older)
+        for tx_name in ("Transmission Weight", "Transmission"):
+            if tx_name in bsdf.inputs:
+                entry["transmission"] = round(bsdf.inputs[tx_name].default_value, 4)
+                break
+        if "IOR" in bsdf.inputs:
+            entry["ior"] = round(bsdf.inputs["IOR"].default_value, 4)
+    else:
+        # Fallback: use viewport diffuse_color (already sRGB)
+        dc = mat.diffuse_color
+        entry["base_color"] = [round(dc[0], 4), round(dc[1], 4), round(dc[2], 4)]
+
+    return entry
+
+
 def main() -> None:
     argv = sys.argv
     if "--" not in argv:
@@ -27,7 +85,9 @@ def main() -> None:
 
     bpy.ops.wm.open_mainfile(filepath=blend_path)
 
-    materials = [m.name for m in bpy.data.materials if m.asset_data is not None]
+    materials = [
+        _extract_pbr(m) for m in bpy.data.materials if m.asset_data is not None
+    ]
     node_groups = [ng.name for ng in bpy.data.node_groups if ng.asset_data is not None]
 
     catalog = {"materials": materials, "node_groups": node_groups}