iOS: improve QR pairing flow (#51359)

- improve QR pairing UX and bootstrap token handling
- preserve repeated optimistic user messages during refresh
- add regression coverage for refresh reconciliation

Thanks @ImLukeF

src/plugin-sdk/device-bootstrap.ts

@@ -1,4 +1,8 @@
 // Shared bootstrap/pairing helpers for plugins that provision remote devices.
 
 export { approveDevicePairing, listDevicePairing } from "../infra/device-pairing.js";
-export { issueDeviceBootstrapToken } from "../infra/device-bootstrap.js";
+export {
+  clearDeviceBootstrapTokens,
+  issueDeviceBootstrapToken,
+  revokeDeviceBootstrapToken,
+} from "../infra/device-bootstrap.js";