refactor: rename thumbnail_rendering queue to asset_pipeline

The queue handles far more than thumbnails: OCC tessellation, USD master
generation, GLB production, order line renders, and workflow renders.
asset_pipeline better reflects its role as the render-worker's primary queue.

Updated all references in: task decorators, celery_app.py, beat_tasks.py,
docker-compose.yml worker command, worker.py MONITORED_QUEUES, admin.py,
CLAUDE.md, LEARNINGS.md, Dockerfile, helpTexts.ts, test files,
and all .claude/commands/*.md skill files.

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

backend/app/api/routers/admin.py

@@ -366,7 +366,7 @@ async def update_settings(
     await db.commit()
 
     # Note: blender-renderer HTTP service removed; concurrency is now controlled
-    # via render-worker Docker concurrency setting (thumbnail_rendering queue).
+    # via render-worker Docker concurrency setting (asset_pipeline queue).
 
     return _settings_to_out(await _load_settings(db))