feat: deposit module — QR flow, PayDepositPage, BookingDetailPanel widget

- Backend: GET /api/pay/:slug (public) — returns active hold confirmation URL
- PayDepositPage: public page /:slug/pay for guests (no login required)
- DepositSettingsPage: QR code section with print button
- BookingDetailPanel: DepositWidget in payment tab
  - Наличными / ЮКасса (QR) buttons
  - hold_created: copy link + refresh
  - hold_confirmed: release form (вернуть / списать)
  - Final status badges

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -13,6 +13,7 @@
     "clsx": "^2.1.1",
     "date-fns": "^3.6.0",
     "lucide-react": "^0.446.0",
+    "qrcode.react": "^4.2.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
     "react-router-dom": "^6.26.0",