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>

backend/app/api/routers/asset_libraries.py

@@ -4,13 +4,15 @@ import shutil
 from pathlib import Path
 
 from fastapi import APIRouter, Depends, HTTPException, UploadFile, File, Form, status
+from fastapi.responses import JSONResponse
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
 from pydantic import BaseModel
 
 from app.database import get_db
+from sqlalchemy import text
 from app.config import settings
-from app.domains.materials.models import AssetLibrary
+from app.domains.materials.models import AssetLibrary, Material, MaterialAlias
 from app.utils.auth import require_admin_or_pm
 
 router = APIRouter(prefix="/asset-libraries", tags=["asset-libraries"])
@@ -58,6 +60,50 @@ def _to_out(lib: AssetLibrary) -> dict:
 
 # ── Endpoints ─────────────────────────────────────────────────────────────────
 
+@router.get("/pbr-map")
+async def get_material_pbr_map(db: AsyncSession = Depends(get_db)):
+    """PBR properties for all materials in the active asset library.
+
+    Public (no auth) — needed by all 3D viewers.
+    Returns keyed by canonical name AND all known aliases so the viewer can
+    look up materials by raw Excel names (e.g. "Steel--Stahl") without needing
+    a separate alias resolution step.
+    """
+    result = await db.execute(
+        select(AssetLibrary).where(AssetLibrary.is_active == True).limit(1)  # noqa: E712
+    )
+    lib = result.scalar_one_or_none()
+    if not lib or not lib.catalog:
+        return JSONResponse(content={}, headers={"Cache-Control": "public, max-age=3600"})
+    materials = lib.catalog.get("materials", [])
+    pbr_map: dict = {}
+    for m in materials:
+        if isinstance(m, str):
+            continue  # old format — skip
+        pbr_map[m["name"]] = {
+            "base_color": m.get("base_color", [0.5, 0.5, 0.5]),
+            "metallic": m.get("metallic", 0.0),
+            "roughness": m.get("roughness", 0.5),
+            "transmission": m.get("transmission", 0.0),
+            "ior": m.get("ior", 1.45),
+        }
+
+    # Also index by aliases so frontend can look up by raw Excel names
+    # (e.g. "Steel--Stahl" → same PBR as "SCHAEFFLER_010101_Steel-Bare")
+    # Bypass RLS — this is public data and aliases may have NULL tenant_id
+    if pbr_map:
+        await db.execute(text("SET LOCAL app.current_tenant_id = 'bypass'"))
+        alias_result = await db.execute(
+            select(MaterialAlias.alias, Material.name)
+            .join(Material, MaterialAlias.material_id == Material.id)
+        )
+        for alias, canonical_name in alias_result.all():
+            if canonical_name in pbr_map and alias not in pbr_map:
+                pbr_map[alias] = pbr_map[canonical_name]
+
+    return JSONResponse(content=pbr_map, headers={"Cache-Control": "public, max-age=3600"})
+
+
 @router.get("", response_model=list[AssetLibraryOut])
 async def list_asset_libraries(
     db: AsyncSession = Depends(get_db),