Add SUPPORTS_CONCURRENT_SESSIONS=True to PMOpsEnvironment

Each instance has fully isolated state (ticketing/chat/codebase are
per-instance), so concurrent sessions are safe.

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

server/pm_ops_environment.py

@@ -35,6 +35,8 @@ def _oracle_check(scenario: Dict[str, Any]) -> bool:
 
 
 class PMOpsEnvironment:
+    SUPPORTS_CONCURRENT_SESSIONS = True
+
     def __init__(self):
         self._ticketing: Optional[TicketingApp] = None
         self._codebase: Optional[CodebaseApp] = None