fix: use phone-reachable relay URL in wallet-import QR

The "Import from a patient app → QR" code baked the web app's own
API_BASE_URL (typically http://localhost:4000) into the pairing URI, so a
real phone could never reach the relay and "Scan to connect" silently
stalled. Use the backend's server-resolved, device-reachable relay URL
instead (PUBLIC_RELAY_URL, else the request host), surface it on the
WalletPairing type, and document PUBLIC_RELAY_URL in .env.example.

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

frontend/components/patients/import-from-wallet-dialog.tsx

@@ -19,7 +19,7 @@ import {
 } from "@/components/ui/dialog";
 import { Input } from "@/components/ui/input";
 import { Switch } from "@/components/ui/switch";
-import { ApiError, API_BASE_URL } from "@/lib/api-client";
+import { ApiError } from "@/lib/api-client";
 import {
   commitWalletShare,
   type Patient,
@@ -159,7 +159,10 @@ export function ImportFromWalletDialog({
         durationHours: temporary ? durationHours : undefined,
       });
       const params = new URLSearchParams({
-        relay: API_BASE_URL,
+        // Use the server-resolved, phone-reachable relay URL — NOT API_BASE_URL,
+        // which is often http://localhost:4000 (the phone itself) and never
+        // connects from a real device.
+        relay: pairing.relayUrl,
         rid: pairing.id,
         epk: pairing.ephemeralPubKey,
         mode: pairing.shareMode,