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/tests/domains/test_rendering_service.py

@@ -0,0 +1,112 @@
+"""Tests for rendering domain — workflow builder + task helpers."""
+import uuid
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+# ---------------------------------------------------------------------------
+# workflow_builder unit tests (no DB required)
+# ---------------------------------------------------------------------------
+
+def test_dispatch_workflow_unknown_type_raises():
+    from app.domains.rendering.workflow_builder import dispatch_workflow
+    with pytest.raises(ValueError, match="Unknown workflow type"):
+        dispatch_workflow("nonexistent_type", str(uuid.uuid4()))
+
+
+def test_build_still_returns_chain():
+    """_build_still returns a Celery chain wrapping render_order_line_still_task."""
+    from celery import chain
+    from app.domains.rendering.workflow_builder import _build_still
+    canvas = _build_still(str(uuid.uuid4()), {})
+    # A single-task chain is still a Celery Signature, not a plain chain, but
+    # it should be callable / have apply_async
+    assert hasattr(canvas, "apply_async")
+
+
+def test_build_multi_angle_creates_group():
+    """_build_multi_angle returns a Celery group with one sig per angle."""
+    from celery import group
+    from app.domains.rendering.workflow_builder import _build_multi_angle
+    order_line_id = str(uuid.uuid4())
+    canvas = _build_multi_angle(order_line_id, {"angles": [0, 90, 180]})
+    # group has tasks attribute
+    assert hasattr(canvas, "tasks")
+    assert len(canvas.tasks) == 3
+
+
+def test_build_still_with_exports_is_chain():
+    """_build_still_with_exports returns a chain."""
+    from app.domains.rendering.workflow_builder import _build_still_with_exports
+    canvas = _build_still_with_exports(str(uuid.uuid4()), {})
+    assert hasattr(canvas, "apply_async")
+
+
+def test_build_turntable_raises_without_step_path():
+    """_build_turntable raises ValueError if step_path missing in params."""
+    from app.domains.rendering.workflow_builder import _build_turntable
+    with pytest.raises(ValueError, match="step_path"):
+        _build_turntable(str(uuid.uuid4()), {})
+
+
+def test_build_turntable_raises_without_output_dir():
+    from app.domains.rendering.workflow_builder import _build_turntable
+    with pytest.raises(ValueError, match="output_dir"):
+        _build_turntable(str(uuid.uuid4()), {"step_path": "/tmp/test.stp"})
+
+
+# ---------------------------------------------------------------------------
+# _resolve_step_path_for_order_line — unit-tests with DB (integration)
+# ---------------------------------------------------------------------------
+
+@pytest.mark.integration
+@pytest.mark.asyncio
+async def test_resolve_step_path_returns_none_for_missing_line(db):
+    """Returns (None, None) for a line_id that doesn't exist."""
+    from app.domains.rendering.tasks import _resolve_step_path_for_order_line
+    import asyncio
+
+    result = _resolve_step_path_for_order_line(str(uuid.uuid4()))
+    assert result == (None, None)
+
+
+# ---------------------------------------------------------------------------
+# publish_asset (unit test with mocked DB)
+# ---------------------------------------------------------------------------
+
+def test_publish_asset_signature():
+    """publish_asset is importable and is a bound Celery task."""
+    from app.domains.rendering.tasks import publish_asset
+    assert callable(publish_asset)
+    assert hasattr(publish_asset, "delay")
+
+
+# ---------------------------------------------------------------------------
+# generate_gltf_geometry_task — smoke test (unit)
+# ---------------------------------------------------------------------------
+
+def test_generate_gltf_geometry_task_importable():
+    from app.tasks.step_tasks import generate_gltf_geometry_task
+    assert callable(generate_gltf_geometry_task)
+    assert hasattr(generate_gltf_geometry_task, "delay")
+
+
+# ---------------------------------------------------------------------------
+# New order-line tasks are importable and correctly registered
+# ---------------------------------------------------------------------------
+
+def test_render_order_line_still_task_importable():
+    from app.domains.rendering.tasks import render_order_line_still_task
+    assert render_order_line_still_task.name == "app.domains.rendering.tasks.render_order_line_still_task"
+    assert render_order_line_still_task.queue == "thumbnail_rendering"
+
+
+def test_export_gltf_for_order_line_task_importable():
+    from app.domains.rendering.tasks import export_gltf_for_order_line_task
+    assert export_gltf_for_order_line_task.queue == "thumbnail_rendering"
+
+
+def test_export_blend_for_order_line_task_importable():
+    from app.domains.rendering.tasks import export_blend_for_order_line_task
+    assert export_blend_for_order_line_task.queue == "thumbnail_rendering"