Fix DogExecutor to use new process() API instead of effect_dog()

The dog effect was updated to use process() but DogExecutor
was still importing the old effect_dog() function.

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

legacy_tasks.py

@@ -88,10 +88,10 @@ class DogExecutor(Executor):
     """Executor for the dog effect."""
 
     def execute(self, config: Dict, inputs: List[Path], output_path: Path) -> Path:
-        from effect import effect_dog
+        from effect import process as dog_process
         if len(inputs) != 1:
             raise ValueError(f"Dog effect expects 1 input, got {len(inputs)}")
-        return effect_dog(inputs[0], output_path, config)
+        return dog_process(inputs, output_path, config, None)
 
 
 @register_executor("effect:identity")