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>

frontend/src/__tests__/pages/WorkerActivity.test.tsx

@@ -25,18 +25,18 @@ describe('worker API types', () => {
   test('CeleryWorker interface shape', () => {
     const worker = {
       name: 'celery@worker1',
-      queues: ['thumbnail_rendering'],
+      queues: ['asset_pipeline'],
       active_task_count: 2,
       active_tasks: [{ name: 'render_still_task', id: 'abc' }],
       total_tasks_processed: { render_still_task: 42 },
     }
-    expect(worker.queues).toContain('thumbnail_rendering')
+    expect(worker.queues).toContain('asset_pipeline')
     expect(worker.active_tasks).toHaveLength(1)
   })
 
   test('QueueStatus interface shape', () => {
     const qs = {
-      queue_depths: { step_processing: 3, thumbnail_rendering: 0 },
+      queue_depths: { step_processing: 3, asset_pipeline: 0 },
       pending_count: 3,
       active: [],
       reserved: [],