Fix: Proper session cleanup in LeaveLobby

- Clear clientSteamIds dictionary on disconnect
- Reset loadingSave flag to false
- Prevents stale data when rejoining servers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

RiptideSteamTransport/LobbyManager.cs

@@ -159,15 +159,17 @@ namespace Riptide.Demos.Steam.PlayerHosted
 
             Main.helper.Log("clear players");
             Main.kCPlayers.Clear();
+            Main.clientSteamIds.Clear();  // Clear client-to-steam ID mapping
             LobbyHandler.ClearPlayerList();
             LobbyHandler.ClearChatEntries();
             Main.helper.Log("end clear players");
 
+            // Reset loading state
+            loadingSave = false;
+
             if (KCServer.IsRunning)
                 KCServer.server.Stop();
 
-
-
             Main.TransitionTo(MenuState.ServerBrowser);
             ServerBrowser.registerServer = false;
         }