Title: World unload stalls while waiting for DLC banner HTTP downloads (1.210.014, no mods)

Observed behavior
After creating/loading a Star System world and choosing Save and Exit to Main Menu, the game remains on the world progress dialog for several minutes. Saving completes, but returning to the main menu is blocked.

Environment
Space Engineers PC, App Version 01_210_014; Windows 11 x64; .NET Framework 4.8.9363.0. The affected session log explicitly reports "List of used mods (0)" and its saved world configuration contains <Mods />. Experimental mode is enabled. No claim is made about installation integrity; the log also contains missing vanilla music asset warnings.

Observed sequence (2026-11-07, UTC+8)
13:43:54.938: UnloadAndExitToMenu - Started
13:43:54.990: Session snapshot save - END
The save files were verified on disk with matching timestamps.
From 13:43:59 onward, managed threads 9 and 10 continue downloading promo ZIP files from https://crashlogs.keenswh.com/api/banner/ (Prosperity, Economy2, CoreSystems, ApexSurvival, Fieldwork and Contact banners). The unload was still waiting when live thread stacks were captured several minutes later.

Main thread stack (abbreviated, captured from the affected process)
System.Threading.WaitHandle.WaitAll
ParallelTasks.Parallel.WaitForAll
ParallelTasks.PrioritizedScheduler.WaitForTasksToFinish
Sandbox.Game.World.MySession.Unload
Sandbox.Game.World.MySessionLoader.Unload
Sandbox.Game.World.MySessionLoader.UnloadAndExitToMenu

Both managed worker threads 9 and 10 (abbreviated)
System.Threading.WaitHandle.WaitOne
RestSharp.AsyncHelpers.CustomSynchronizationContext.Run
RestSharp.AsyncHelpers.RunSync
VRage.Platform.Windows.Http.MyWindowsHttpClient.DownloadAsync
Sandbox.Game.Screens.MyGuiScreenMainMenuBase.DownloadPromoZip
Sandbox.Game.Screens.Helpers.MyGuiControlDLCBanners.DownloadImages
ParallelTasks.DelegateWork.DoWork
ParallelTasks.WorkItem.DoWork
ParallelTasks.PrioritizedScheduler.Worker.WorkerLoop

Expected behavior
World unloading should complete without waiting for optional promotional images. Slow or unavailable banner downloads should have bounded timeouts and cancellation, and should not block session teardown.

Assessment / limits
The captured stacks strongly indicate that optional DLC banner network tasks are delaying session teardown. This was one observed session; repeatability, the exact network failure mode and eventual completion time have not been established. This is reported as a prolonged stall, not a proven permanent deadlock.

Suggested reproduction (not independently validated)
Start the game with banner downloads slow/unavailable, enter a new unmodded Star System world promptly, then Save and Exit to Main Menu while those downloads are still outstanding.
