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/messages/en.json

@@ -69,6 +69,8 @@
   },
   "nav": {
     "aria": "Main navigation",
+    "collapseSidebar": "Collapse sidebar",
+    "expandSidebar": "Expand sidebar",
     "groups": {
       "operations": "Daily operations",
       "menuSales": "Menu & sales",
@@ -1017,7 +1019,28 @@
     "featureOff": "Not included — upgrade",
     "featureMenu3dUpgrade": "3D menu is available on Pro and higher plans.",
     "featureMenuAi3d": "AI 3D generation",
-    "featureMenuAi3dUpgrade": "AI 3D generation is on Business and Enterprise (100 per month)."
+    "featureMenuAi3dUpgrade": "AI 3D generation is on Business and Enterprise (100 per month).",
+    "checkout": {
+      "title": "Invoice & Payment",
+      "subtitle": "Review your order and pay",
+      "backToPlans": "Back to plans",
+      "invalidPlan": "The selected plan is not available for online purchase.",
+      "invoiceLabel": "Proforma invoice",
+      "invoiceNo": "Invoice no.",
+      "issuedAt": "Issued",
+      "billingPeriod": "Billing period",
+      "monthsCount": "{count} mo",
+      "description": "Description",
+      "qty": "Qty",
+      "unitPrice": "Unit price",
+      "amount": "Amount",
+      "planLine": "{plan} plan subscription",
+      "subtotal": "Subtotal",
+      "total": "Amount due",
+      "secureNote": "Payment is processed through a secure bank gateway.",
+      "payTotal": "Pay {total}",
+      "redirecting": "Redirecting to gateway..."
+    }
   },
   "settings": {
     "title": "Settings",