feat(N): workflow pipeline, 3D viewer, worker management, QC tests

- workflow_builder.py: fix broken stubs, add render_order_line_still_task
  (resolves step_path from DB instead of passing order_line_id as step_path)
- domains/rendering/tasks.py: add render_order_line_still_task,
  export_gltf_for_order_line_task, export_blend_for_order_line_task,
  generate_gltf_geometry_task (trimesh STL→GLB, no Blender needed)
- tasks/step_tasks.py: add generate_gltf_geometry_task for CadFile GLB export
- cad router: POST /{id}/generate-gltf-geometry endpoint (admin/PM)
- worker router: GET /celery-workers + POST /scale (docker compose subprocess)
- Dockerfile: pip install -e "[dev]" to enable pytest
- docker-compose.yml: docker socket + compose file mount on backend
- ThreeDViewer.tsx: mode toggle (geometry/production), wireframe, env presets,
  download buttons (GLB + .blend)
- CadPreview.tsx: load gltf_geometry/gltf_production/blend_production assets
  from MediaAsset table and pass URLs to ThreeDViewer
- ProductDetail.tsx: "View 3D" button → /cad/:id, "Generate GLB" button
- media router/service: cad_file_id filter on GET /api/media
- WorkerManagement.tsx: new page with worker status, queue depth, scale controls
- App.tsx + Layout.tsx: /workers route + sidebar link (admin/PM)
- tests: test_rendering_service.py, test_orders_service.py (backend)
- tests: WorkerActivity.test.tsx, WorkerManagement.test.tsx (frontend)

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

backend/app/api/routers/cad.py

@@ -320,6 +320,38 @@ async def generate_stl(
     return {"status": "queued", "task_id": task.id, "quality": quality}
 
 
+@router.post("/{id}/generate-gltf-geometry", status_code=status.HTTP_202_ACCEPTED)
+async def generate_gltf_geometry(
+    id: uuid.UUID,
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Queue GLB geometry export from the existing STL cache (trimesh, no Blender).
+
+    Stores the result as a MediaAsset with asset_type='gltf_geometry'.
+    The STL low-quality cache must already exist (run a thumbnail render first).
+    """
+    if user.role.value not in ("admin", "project_manager"):
+        raise HTTPException(status_code=403, detail="Insufficient permissions")
+
+    cad = await _get_cad_file(id, db)
+    if not cad.stored_path:
+        raise HTTPException(status_code=404, detail="STEP file not uploaded for this CAD file")
+
+    step_path = Path(cad.stored_path)
+    stl_path = step_path.parent / f"{step_path.stem}_low.stl"
+    if not stl_path.exists():
+        raise HTTPException(
+            status_code=404,
+            detail="STL low-quality cache not found. Trigger a render first to generate it.",
+        )
+
+    # Queue as a thumbnail_rendering task (trimesh available in render-worker)
+    from app.tasks.step_tasks import generate_gltf_geometry_task
+    task = generate_gltf_geometry_task.delay(str(id))
+    return {"status": "queued", "task_id": task.id, "cad_file_id": str(id)}
+
+
 @router.post(
     "/{id}/regenerate-thumbnail",
     status_code=status.HTTP_202_ACCEPTED,