feat: QR pairing for wallet import (backend + website)

- Backend: nullable wallet_number on wallet_share_requests (migration 0029);
  createPairingRequest + POST /api/patients/wallet/pair; applyShareResponse
  binds the authenticated wallet on QR (pairing) requests
- Frontend: Import dialog gains a "Show QR" mode rendering a temetro-pair QR
  (react-qr-code) the patient scans; requestWalletPairing helper; i18n keys

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

frontend/lib/i18n/locales/en/translation.json

@@ -186,6 +186,11 @@
     "importApp": {
       "title": "Import from a patient app",
       "description": "Enter the patient's wallet number. They'll get a request on their phone to approve sharing their record with this clinic.",
+      "tabNumber": "By number",
+      "tabQr": "Show QR",
+      "qrHint": "Generate a QR code, then have the patient scan it in their wallet app to share their record.",
+      "qrCaption": "Scan this in the patient app",
+      "generateQr": "Show QR code",
       "walletLabel": "Patient wallet number",
       "walletPlaceholder": "tmw_…",
       "tempLabel": "Share temporarily",