fix(gateway): trigger memory provider shutdown on /new and /reset

The /new and /reset commands were not calling shutdown_memory_provider()
on the cached agent before eviction. This caused OpenViking (and any
memory provider that relies on session-end shutdown) to skip commit,
leaving memories un-indexed until idle timeout or gateway shutdown.

Add the missing shutdown_memory_provider() call in _handle_reset_command(),
matching the behavior already present in the session expiry watcher.

Fixes #7759

gateway/run.py

@@ -3971,6 +3971,11 @@ class GatewayRunner:
                 _cached = self._agent_cache.get(session_key)
                 _old_agent = _cached[0] if isinstance(_cached, tuple) else _cached if _cached else None
             if _old_agent is not None:
+                try:
+                    if hasattr(_old_agent, "shutdown_memory_provider"):
+                        _old_agent.shutdown_memory_provider()
+                except Exception:
+                    pass
                 try:
                     if hasattr(_old_agent, "close"):
                         _old_agent.close()