feat: QR code on printed shopping lists

Added the qrcode package (server-side data-URL generation, no client
JS) rather than hand-rolling QR encoding. Only rendered when the list
is public — a private list's /s/ link 404s for anyone who isn't the
owner, so a QR code there would just be a dead scan.

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

apps/web/messages/fr.json

@@ -896,6 +896,8 @@
   "shoppingLists": {
     "title": "Listes de courses",
     "subtitle": "Planifiez vos courses",
+    "qrCodeAlt": "Code QR menant à cette liste de courses",
+    "qrCodeCaption": "Scannez pour voir en ligne",
     "empty": "Aucune liste de courses",
     "emptyDescription": "Générez-en une depuis un planning repas, ou créez-en une de zéro.",
     "listEmpty": "Vide",