fix: media thumbnails, product dimensions, inline 3D viewer, GLB export

Bug A: Media Library thumbnails were gray because <img src> cannot send
JWT auth headers. Added useAuthBlob() hook (fetch + createObjectURL) in
MediaBrowser.tsx. Also fixed publish_asset Celery task to populate
product_id + cad_file_id on MediaAsset for thumbnail fallback resolution.

Bug B: Product dimensions now shown in Product Details card with Ruler
icon and "from CAD" label when cad_mesh_attributes.dimensions_mm exists.

Bug C: Replaced 128×128 CAD thumbnail with InlineCadViewer component.
Queries gltf_geometry MediaAssets, fetches GLB via auth fetch → blob URL
→ Three.js Canvas with OrbitControls. Falls back to thumbnail + "Load 3D
Model" button. Polling when GLB generation is in progress.

Bug D: trimesh was in [cad] optional extra but Dockerfile only installed
[dev]. Changed to pip install -e ".[dev,cad]" — trimesh now available in
backend container, GLB + Colors export works.

Also added bbox extraction (STL-first numpy parsing) in render_step_thumbnail
and admin "Re-extract CAD Metadata" bulk endpoint.

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

backend/app/services/step_processor.py

@@ -293,8 +293,33 @@ def extract_mesh_edge_data(step_path: str) -> dict:
             except Exception:
                 continue
 
+        # Bounding box extraction (OCC Bnd_Box)
+        from OCC.Core.Bnd import Bnd_Box
+        from OCC.Core.BRepBndLib import brepbndlib
+        try:
+            bbox = Bnd_Box()
+            brepbndlib.Add(shape, bbox)
+            xmin, ymin, zmin, xmax, ymax, zmax = bbox.Get()
+            dimensions_mm = {
+                "x": round(xmax - xmin, 2),
+                "y": round(ymax - ymin, 2),
+                "z": round(zmax - zmin, 2),
+            }
+            bbox_center_mm = {
+                "x": round((xmin + xmax) / 2, 2),
+                "y": round((ymin + ymax) / 2, 2),
+                "z": round((zmin + zmax) / 2, 2),
+            }
+        except Exception:
+            dimensions_mm = None
+            bbox_center_mm = None
+
         if not dihedral_angles:
-            return {}
+            result: dict = {}
+            if dimensions_mm:
+                result["dimensions_mm"] = dimensions_mm
+                result["bbox_center_mm"] = bbox_center_mm
+            return result
 
         import statistics
         median_angle = statistics.median(dihedral_angles)
@@ -307,11 +332,15 @@ def extract_mesh_edge_data(step_path: str) -> dict:
         else:
             suggested = 30.0
 
-        return {
+        result = {
             "suggested_smooth_angle": round(suggested, 1),
             "has_mechanical_edges": max_angle > 45,
             "sharp_edge_midpoints": sharp_midpoints[:500],
         }
+        if dimensions_mm:
+            result["dimensions_mm"] = dimensions_mm
+            result["bbox_center_mm"] = bbox_center_mm
+        return result
     except ImportError:
         # OCC not available (e.g. in backend container)
         return {}