Don't push history when we've gotten here via popstate

frontend/src/hooks/useAppShell.ts

@@ -89,7 +89,9 @@ export function useAppShell(): UseAppShellResult {
     const handlePopstate = () => {
       const section = parseHashSettingsSection();
       if (section !== null) {
-        pushedSettingsEntryRef.current = true;
+        // Don't set pushedSettingsEntryRef here — the user arrived via
+        // back/forward, not by opening settings.  Closing settings should
+        // replaceState, not history.back(), to avoid popping an unrelated entry.
         startTransition(() => {
           setShowSettings(true);
           setSettingsSection(section);