Adjust admin layout for better mobile responsiveness

Modify `admin.tsx` to make the SheetContent component take full width on small screens and maintain its size on larger breakpoints.

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artifacts/teaboy-os/src/pages/admin.tsx

@@ -223,7 +223,7 @@ export default function AdminPage() {
               <MenuIcon size={20} />
             </button>
           </SheetTrigger>
-          <SheetContent side={isRtl ? "right" : "left"} className="w-72 p-4">
+          <SheetContent side={isRtl ? "right" : "left"} className="w-full sm:w-72 p-4">
             <div className="flex items-center gap-2 mb-4 mt-2">
               <Settings size={18} className="text-red-400" />
               <h2 className="font-semibold text-foreground">{t("admin.title")}</h2>