Enhance InvoicesPage with additional button for client management

- Added a secondary button for "Add Client" alongside the "New Invoice" button to improve user functionality and streamline invoice management.

frontend-web/src/pages/InvoicesPage.tsx

@@ -27,7 +27,10 @@ export default function InvoicesPage() {
       {/* Header */}
       <div className="mb-5 flex items-center justify-between">
         <h1 className="text-xl font-medium">Invoices</h1>
-        <Button size="sm">New Invoice</Button>
+        <div className="flex gap-2">
+          <Button variant="secondary" size="sm">Add Client</Button>
+          <Button size="sm">New Invoice</Button>
+        </div>
       </div>
 
       {/* Summary Cards */}