Add delete action to invitations and UI improvements

Introduces a delete button for unused invitations in InvitationsListCard, allowing admins to remove invites. Also improves layout and spacing in the invitations card, formats order totals with currency in RecentOrdersCard, and hides several unused cards in the admin page as requested.

components/admin/RecentOrdersCard.tsx

@@ -54,7 +54,7 @@ export default function RecentOrdersCard() {
                 <div className="text-muted-foreground">{new Date(o.createdAt).toLocaleString()}</div>
               </div>
               <div className="mt-1 text-xs text-muted-foreground">
-                User: {o.userId} · Total: {o.total}
+                User: {o.userId} · Total: £{Number(o.total).toFixed(2)}
               </div>
               {o.items && o.items.length > 0 && (
                 <ul className="mt-2 text-xs list-disc pl-4 text-muted-foreground">