feat: GPU rendering + material matching + perf improvements

- GPU: fix Cycles device activation order — set compute_device_type
  BEFORE engine init, re-set AFTER open_mainfile wipes preferences
- GPU: remove _mark_sharp_and_seams edit-mode loop (redundant with
  Blender 5.0 shade_smooth_by_angle), saves ~200s/render on 175 parts
- Material: fix _AFN suffix mismatch — build AF-stripped mat_map keys
  and add prefix fallback in _apply_material_library (blender_render.py)
- Material: production GLB now uses get_material_library_path() which
  checks active AssetLibrary instead of empty legacy system setting
- Admin: RenderTemplateTable multi-select output types (M2M frontend)
- Admin: MaterialLibraryPanel replaced with link to Asset Libraries
- UX: move Toaster to top-left to avoid dispatch button overlap
- SQLAlchemy: add .unique() to all RenderTemplate M2M collection queries
- Logging: flush=True on all Blender progress prints, stdout reconfigure

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

backend/app/tasks/celery_app.py

@@ -34,5 +34,9 @@ celery_app.conf.update(
             "task": "app.tasks.beat_tasks.broadcast_queue_status",
             "schedule": 10.0,  # every 10 seconds
         },
+        "recover-stuck-cad-files-every-5m": {
+            "task": "app.tasks.beat_tasks.recover_stuck_cad_files",
+            "schedule": 300.0,  # every 5 minutes
+        },
     },
 )