feat(settings): Session tabs toggle in General → Navigation

A new Session tabs group (web/desktop only) turns the header session
tabs off; disabled, the header renders the exact pre-tabs view — plain
session title with meta row and the always-visible session menu (the
same block VS Code uses). The Alt+W close-tab shortcut no-ops while
tabs are off. Registered in settings search with a matching anchor;
labels translated in all locales.

packages/ui/src/hooks/useKeyboardShortcuts.ts

@@ -300,7 +300,7 @@ export const useKeyboardShortcuts = () => {
         return;
       }
 
-      if (!isVSCodeRuntime() && eventMatchesShortcut(e, combo('close_session_tab'))) {
+      if (!isVSCodeRuntime() && useUIStore.getState().sessionTabsEnabled && eventMatchesShortcut(e, combo('close_session_tab'))) {
         e.preventDefault();
         if (currentSessionId) {
           closeSessionTabAndActivateNeighbour(currentSessionId);