feat(02-02): add admin client list page and create-client flow

- /admin page: Server Component fetching all clients with payment badges
- ClientRow component with Acconto/Saldo status badges and secret link
- /admin/clients/new: form wired to createClient Server Action
- createClient action: Zod validation, inserts client + 2 payment stubs (Acconto 50%, Saldo 50%)
- Token auto-generated server-side via nanoid $defaultFn
- Redirects to /admin/clients/[id] after creation; revalidates /admin

src/app/admin/page.tsx

@@ -0,0 +1,64 @@
+import Link from "next/link";
+import { getAllClientsWithPayments } from "@/lib/admin-queries";
+import { ClientRow } from "@/components/admin/ClientRow";
+import { Button } from "@/components/ui/button";
+
+export const revalidate = 0; // always fresh — admin needs real-time data
+
+export default async function AdminDashboard() {
+  const clients = await getAllClientsWithPayments();
+
+  return (
+    <div>
+      <div className="flex items-center justify-between mb-6">
+        <h1 className="text-2xl font-bold text-gray-900">Clienti</h1>
+        <Button asChild>
+          <Link href="/admin/clients/new">+ Nuovo cliente</Link>
+        </Button>
+      </div>
+
+      {clients.length === 0 ? (
+        <div className="text-center py-20 text-gray-400">
+          <p>Nessun cliente ancora.</p>
+          <p className="mt-2">
+            <Link
+              href="/admin/clients/new"
+              className="text-blue-600 hover:underline"
+            >
+              Crea il primo cliente
+            </Link>
+          </p>
+        </div>
+      ) : (
+        <div className="bg-white rounded-lg border border-gray-200 overflow-hidden">
+          <table className="w-full text-sm">
+            <thead className="bg-gray-50 border-b border-gray-200">
+              <tr>
+                <th className="text-left py-3 px-4 font-medium text-gray-600">
+                  Cliente
+                </th>
+                <th className="text-left py-3 px-4 font-medium text-gray-600">
+                  Totale
+                </th>
+                <th className="text-left py-3 px-4 font-medium text-gray-600">
+                  Acconto
+                </th>
+                <th className="text-left py-3 px-4 font-medium text-gray-600">
+                  Saldo
+                </th>
+                <th className="text-left py-3 px-4 font-medium text-gray-600">
+                  Link
+                </th>
+              </tr>
+            </thead>
+            <tbody>
+              {clients.map((client) => (
+                <ClientRow key={client.id} client={client} />
+              ))}
+            </tbody>
+          </table>
+        </div>
+      )}
+    </div>
+  );
+}