Fix Celery workers to use Redis for shared cache index

The get_cache_manager() singleton wasn't initializing with Redis,
so workers couldn't see files uploaded via the API server.

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

cache_manager.py

@@ -757,9 +757,24 @@ def get_cache_manager() -> L1CacheManager:
     """Get the singleton cache manager instance."""
     global _manager
     if _manager is None:
+        import redis
+        from urllib.parse import urlparse
+
         cache_dir = Path(os.environ.get("CACHE_DIR", str(Path.home() / ".artdag" / "cache")))
         l2_server = os.environ.get("L2_SERVER", "http://localhost:8200")
-        _manager = L1CacheManager(cache_dir=cache_dir, l2_server=l2_server)
+
+        # Initialize Redis client for shared cache index
+        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),
+            socket_timeout=5,
+            socket_connect_timeout=5
+        )
+
+        _manager = L1CacheManager(cache_dir=cache_dir, l2_server=l2_server, redis_client=redis_client)
     return _manager