feat(llm): add run_llm_pipeline() stub with correct return shape for Person 3

llm/pipeline.py

@@ -0,0 +1,11 @@
+from typing import Any
+
+async def run_llm_pipeline(action: Any, conversation_history: list[dict]) -> dict[str, Any]:
+    """Person 3's LLM pipeline stub."""
+    return {
+        "defender_response": "I cannot fulfill this request.",
+        "attack_success":    0.1,
+        "safety_flagged":    False,
+        "defense_score":     0.9,
+        "llm_grade":         {"overall": 1.0},
+    }