feat: Docker support for L1 server

- Dockerfile for L1 server/worker
- docker-compose.yml with Redis
- Environment variables for Redis URL and cache dir

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

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

celery_app.py

@@ -5,12 +5,15 @@ Distributed rendering for the Art DAG system.
 Uses the foundational artdag language from GitHub.
 """
 
+import os
 from celery import Celery
 
+REDIS_URL = os.environ.get('REDIS_URL', 'redis://localhost:6379/5')
+
 app = Celery(
     'art_celery',
-    broker='redis://localhost:6379/5',
-    backend='redis://localhost:6379/5',
+    broker=REDIS_URL,
+    backend=REDIS_URL,
     include=['tasks']
 )