Pause screen: Update the save state slots when a save finishes writing

Saves are written on a worker thread, so a state saved just before opening the pause
menu may not be on disk yet when the slots are listed, and the slot stayed empty.
Post SAVESTATE_SLOT_SAVED when a slot save is written, and recreate the pause
screen's views on it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Core/SaveState.cpp

@@ -1174,6 +1174,8 @@ int g_screenshotFailures;
 					g_Config.Save("Saving config for savestate last save undo");
 				}
 				g_filesStale = true;
+				// The pause screen may have listed the slots before the file was there.
+				System_PostUIMessage(UIMessage::SAVESTATE_SLOT_SAVED);
 			}
 		} else {
 			if (result == CChunkFileReader::ERROR_BROKEN_STATE) {