feat: add admin subscriptions management page with new Stripe service and sidebar navigation.

src/components/Sidebar.tsx

@@ -74,6 +74,20 @@ const menuItems = [
       </svg>
     ),
   },
+  {
+    name: 'Subscriptions',
+    href: '/dashboard/subscriptions',
+    icon: (
+      <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+        <path
+          strokeLinecap="round"
+          strokeLinejoin="round"
+          strokeWidth={2}
+          d="M3 10h18M7 15h1m4 0h1m-7 4h12a3 3 0 003-3V8a3 3 0 00-3-3H6a3 3 0 00-3 3v8a3 3 0 003 3z"
+        />
+      </svg>
+    ),
+  },
   {
     name: 'Support Chat',
     href: '/dashboard/support-chat',