qr-plus authenticates to the monolith with a billing service key, not an
identity key, so the modal's top-up now goes through BillingClient::topup ->
POST /api/billing/topup. Drops the unused IdentityClient::walletTopup.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Utility QR types only (URL, WiFi, link list, business, app download) with
SSO, Billing API integration, public /q resolver, and qr-plus:import for
platform migration. vCard and commerce types stay on the platform.
Co-authored-by: Cursor <cursoragent@cursor.com>