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>

backend/drizzle/0029_tiny_starhawk.sql

@@ -0,0 +1 @@
+ALTER TABLE "wallet_share_requests" ALTER COLUMN "wallet_number" DROP NOT NULL;

backend/drizzle/meta/_journal.json

@@ -204,6 +204,13 @@
       "when": 1782052852524,
       "tag": "0028_military_cyclops",
       "breakpoints": true
+    },
+    {
+      "idx": 29,
+      "version": "7",
+      "when": 1782057030557,
+      "tag": "0029_tiny_starhawk",
+      "breakpoints": true
     }
   ]
 }