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>

server.py

@@ -21,16 +21,23 @@ from fastapi.responses import FileResponse
 from pydantic import BaseModel
 
 import redis
+from urllib.parse import urlparse
 
 from celery_app import app as celery_app
 from tasks import render_effect
 
-# Cache directory
-CACHE_DIR = Path.home() / ".artdag" / "cache"
+# Cache directory (use /data/cache in Docker, ~/.artdag/cache locally)
+CACHE_DIR = Path(os.environ.get("CACHE_DIR", str(Path.home() / ".artdag" / "cache")))
 CACHE_DIR.mkdir(parents=True, exist_ok=True)
 
 # Redis for persistent run storage
-redis_client = redis.Redis(host='localhost', port=6379, db=5)
+REDIS_URL = os.environ.get('REDIS_URL', 'redis://localhost:6379/5')
+parsed = urlparse(REDIS_URL)
+redis_client = redis.Redis(
+    host=parsed.hostname or 'localhost',
+    port=parsed.port or 6379,
+    db=int(parsed.path.lstrip('/') or 0)
+)
 RUNS_KEY_PREFIX = "artdag:run:"