Add close() method required by openenv create_app validation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/pm_ops_environment.py

@@ -200,3 +200,8 @@ class PMOpsEnvironment:
         if not grader:
             return 0.0
         return grader.grade(final_state, self._org_config, self._scenario)
+
+    def close(self) -> None:
+        self._ticketing = None
+        self._codebase = None
+        self._chat = None