feat: distributed rendering with Celery

- celery_app.py: Celery configuration with Redis broker
- tasks.py: render_effect task with full provenance tracking
- render.py: CLI for submitting render jobs
- Successfully renders cat → dog with provenance chain

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

celery_app.py

@@ -0,0 +1,31 @@
+"""
+Art DAG Celery Application
+
+Distributed rendering for the Art DAG system.
+Uses the foundational artdag language from GitHub.
+"""
+
+from celery import Celery
+
+app = Celery(
+    'art_celery',
+    broker='redis://localhost:6379/5',
+    backend='redis://localhost:6379/5',
+    include=['tasks']
+)
+
+app.conf.update(
+    result_expires=3600,
+    task_serializer='json',
+    accept_content=['json', 'pickle'],  # pickle needed for internal Celery messages
+    result_serializer='json',
+    event_serializer='json',
+    timezone='UTC',
+    enable_utc=True,
+    task_track_started=True,
+    task_acks_late=True,
+    worker_prefetch_multiplier=1,
+)
+
+if __name__ == '__main__':
+    app.start()