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>

frontend/src/api/worker.ts

@@ -123,3 +123,46 @@ export async function cancelTask(taskId: string): Promise<{ revoked: string }> {
   const res = await api.post<{ revoked: string }>(`/worker/queue/cancel/${taskId}`)
   return res.data
 }
+
+// ---------------------------------------------------------------------------
+// Worker management
+// ---------------------------------------------------------------------------
+
+export interface CeleryWorkerTask {
+  name: string
+  id: string
+}
+
+export interface CeleryWorker {
+  name: string
+  queues: string[]
+  active_task_count: number
+  active_tasks: CeleryWorkerTask[]
+  total_tasks_processed: Record<string, number>
+}
+
+export interface CeleryWorkersResponse {
+  workers: CeleryWorker[]
+  error?: string
+}
+
+export interface ScaleRequest {
+  service: 'render-worker' | 'worker' | 'worker-thumbnail'
+  count: number
+}
+
+export interface ScaleResponse {
+  service: string
+  count: number
+  status: string
+}
+
+export async function getCeleryWorkers(): Promise<CeleryWorkersResponse> {
+  const res = await api.get<CeleryWorkersResponse>('/worker/celery-workers')
+  return res.data
+}
+
+export async function scaleWorkers(req: ScaleRequest): Promise<ScaleResponse> {
+  const res = await api.post<ScaleResponse>('/worker/scale', req)
+  return res.data
+}