feat: pagina Clienti redesign Quiet Luxury — tabella tokenizzata + copia link

- /admin/clients replica design-reference/pagina-clienti (dual light/dark via token)
- ClientRow: colonne numeriche font-mono right-aligned, incassato come pill emerald,
  cella "Link profilo" con pill mono troncata + CopyLinkButton
- nuovo primitivo CopyLinkButton (copia URL assoluto, feedback check emerald)
- PageHeader con sottotitolo + footer conteggio clienti
- DESIGN-SYSTEM.md: inventory (CopyLinkButton, ClientRow) + note pagina Clienti

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/admin/CopyLinkButton.tsx

@@ -0,0 +1,34 @@
+"use client";
+
+import { useState } from "react";
+
+export function CopyLinkButton({ path, title = "Copia link" }: { path: string; title?: string }) {
+  const [copied, setCopied] = useState(false);
+
+  function handleCopy() {
+    const url = typeof window !== "undefined" ? `${window.location.origin}${path}` : path;
+    navigator.clipboard?.writeText(url).then(() => {
+      setCopied(true);
+      setTimeout(() => setCopied(false), 1500);
+    });
+  }
+
+  return (
+    <button
+      type="button"
+      onClick={handleCopy}
+      title={copied ? "Copiato!" : title}
+      className="p-1 rounded text-muted-foreground hover:text-foreground hover:bg-muted transition-colors"
+    >
+      {copied ? (
+        <svg className="w-4 h-4 text-emerald-600 dark:text-emerald-400" fill="none" stroke="currentColor" strokeWidth={2} viewBox="0 0 24 24">
+          <path strokeLinecap="round" strokeLinejoin="round" d="M4.5 12.75l6 6 9-13.5" />
+        </svg>
+      ) : (
+        <svg className="w-4 h-4" fill="none" stroke="currentColor" strokeWidth={1.8} viewBox="0 0 24 24">
+          <path strokeLinecap="round" strokeLinejoin="round" d="M8 5H6a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2v-1M8 5a2 2 0 002 2h2a2 2 0 002-2M8 5a2 2 0 012-2h2a2 2 0 012 2m0 0h2a2 2 0 012 2v3m2 4H10m0 0l3-3m-3 3l3 3" />
+        </svg>
+      )}
+    </button>
+  );
+}