Add dashboard chrome to POS and collapsible sidebar

Wrap the POS terminal in the sidebar + topbar layout via a nested
fullscreen layout, and make the sidebar collapse to an icon-only rail
with a persisted toggle so operators keep navigation on the POS screen.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/dashboard/src/components/pos/pos-screen.tsx

@@ -7,7 +7,6 @@ import { useTranslations, useLocale } from "next-intl";
 import {
   ChevronLeft,
   ChevronRight,
-  LayoutDashboard,
   Minus,
   Package,
   Plus,
@@ -902,17 +901,6 @@ export function PosScreen() {
         </Button>
 
         <div className="flex-1" />
-
-        {/* Dashboard shortcut — only visible to Owner / Manager */}
-        {isManager && (
-          <a
-            href="/"
-            className="flex items-center gap-1.5 rounded-lg px-2.5 py-1.5 text-xs text-muted-foreground transition-colors hover:bg-accent hover:text-foreground"
-          >
-            <LayoutDashboard className="size-4" />
-            <span className="hidden sm:inline">{cafeName}</span>
-          </a>
-        )}
       </div>
 
       {/* ── Pay mode ──────────────────────────────────────────────────────── */}