feat(keyboard): add Cmd+./Ctrl+. shortcut to toggle both sidebars

Reassign Cmd+. (Mac) and Ctrl+. (Win/Linux) from toggling the left
sidebar to toggling both sidebars at once. If either is open, both
close; if both are closed, both open. Left sidebar toggle on non-Mac
now uses Ctrl+B to match the Mac Cmd+B binding.

packages/app/src/hooks/use-keyboard-shortcuts.ts

@@ -33,12 +33,14 @@ export function useKeyboardShortcuts({
   toggleAgentList,
   selectedAgentId,
   toggleFileExplorer,
+  toggleBothSidebars,
 }: {
   enabled: boolean;
   isMobile: boolean;
   toggleAgentList: () => void;
   selectedAgentId?: string;
   toggleFileExplorer?: () => void;
+  toggleBothSidebars?: () => void;
 }) {
   const pathname = usePathname();
   const hosts = useHosts();
@@ -228,6 +230,11 @@ export function useKeyboardShortcuts({
         case "sidebar.toggle.left":
           toggleAgentList();
           return true;
+        case "sidebar.toggle.both":
+          if (toggleBothSidebars) {
+            toggleBothSidebars();
+          }
+          return true;
         case "sidebar.toggle.right":
           if (!toggleFileExplorer) {
             return false;