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/Dockerfile

@@ -19,9 +19,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 # Copy docker CLI for worker scaling
 COPY --from=docker-cli /usr/local/bin/docker /usr/local/bin/docker
 
-# Install Python dependencies (including dev extras for pytest)
+# Install Python dependencies (dev + cad extras: pytest, trimesh, pygltflib)
 COPY pyproject.toml .
-RUN pip install --no-cache-dir -e ".[dev]"
+RUN pip install --no-cache-dir -e ".[dev,cad]"
 
 # Copy app code
 COPY . .