Register dog effect for DAG EFFECT nodes

The EFFECT node executor uses register_effect() to look up effects.
Added dog effect registration so DAG recipes can use effect: dog.

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

tasks.py

@@ -22,6 +22,7 @@ from celery_app import app
 from artdag import DAG, Node, NodeType
 from artdag.engine import Engine
 from artdag.executor import register_executor, Executor, get_executor
+from artdag.nodes.effect import register_effect
 import artdag.nodes  # Register all built-in executors (SOURCE, EFFECT, etc.)
 
 # Add effects to path (use env var in Docker, fallback to home dir locally)
@@ -65,6 +66,14 @@ def get_artdag_commit() -> str:
 
 sys.path.insert(0, str(EFFECTS_PATH / "dog"))
 
+# Register the dog effect with the EFFECT executor
+from effect import effect_dog
+
+@register_effect("dog")
+def _dog_effect(input_path: Path, output_path: Path, config: dict) -> Path:
+    """Dog effect wrapper - registered for DAG EFFECT nodes."""
+    return effect_dog(input_path, output_path, config)
+
 
 def file_hash(path: Path) -> str:
     """Compute SHA3-256 hash of a file."""