feat(admin): print/save-as-PDF for transactions and clean print output

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

P0 user feedback asked for PDF export on orders and transactions. Orders already had Print invoice (window.print). Rather than invent a backend PDF endpoint, the browser's print-to-PDF is the export path:

- Transactions list gains a Print button next to CSV export
- Admin shell now hides sidebar/topbar/inspector under @media print, so printing any admin page (order invoice, transactions, analytics) produces a clean document instead of capturing navigation chrome

src/app/features/admin/shell/admin-layout.component.scss

@@ -498,3 +498,17 @@
     background: rgba(0, 0, 0, 0.6);
   }
 }
+
+/* Print: only the page content matters - hide navigation chrome so
+   browser print / save-as-PDF produces a clean document (orders,
+   transactions, analytics). */
+@media print {
+  .admin-layout__sidebar,
+  .admin-layout__topbar,
+  .admin-layout__inspector {
+    display: none !important;
+  }
+  .admin-layout {
+    display: block !important;
+  }
+}