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>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "epicure",
-  "version": "0.21.0",
+  "version": "0.22.0",
   "private": true,
   "scripts": {
     "dev": "pnpm --filter web dev",