feat(graders): add hard_grader scaffold with interface

graders/hard_grader.py

@@ -0,0 +1,7 @@
+"""
+Hard Grader — Full Evaluation
+Novelty, Success, Strategy and Category diversity.
+"""
+def grade_hard(history: list[dict]) -> float:
+    """Scaffold for hard grader."""
+    return 0.0