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/app/_layout.tsx

@@ -264,6 +264,7 @@ function AppContainer({
   const daemons = useHosts();
   const toggleAgentList = usePanelStore((state) => state.toggleAgentList);
   const toggleFileExplorer = usePanelStore((state) => state.toggleFileExplorer);
+  const toggleBothSidebars = usePanelStore((state) => state.toggleBothSidebars);
 
   const isMobile = UnistylesRuntime.breakpoint === "xs" || UnistylesRuntime.breakpoint === "sm";
   const chromeEnabled = chromeEnabledOverride ?? daemons.length > 0;
@@ -274,6 +275,7 @@ function AppContainer({
     toggleAgentList,
     selectedAgentId,
     toggleFileExplorer,
+    toggleBothSidebars,
   });
 
   const containerStyle = useMemo(