Mirror the async-open path for wallet creation. beginOpenExisting() and
beginCreateWallet() now both delegate to beginAsyncLifecycle(bool create),
which runs the backend init on a detached thread and walks the failover
server list (preferred server first, then all usable defaults), reporting
the preferred server's error on total failure. The first-run wizard's
Create button drives this through a non-blocking "creating" poll state so
the UI no longer freezes while the backend contacts a (possibly flaky)
lightwalletd. The created seed response is securely wiped immediately and
read back via exportSeed for the reveal/verify steps.
Safe because litelib_initialize_new contacts the server before writing any
wallet file and LightClient::new errors if a wallet already exists, so a
failed candidate leaves no partial state.
Tests: fake backend's initialize_new now honors the dead/warmup server
substrings; testLiteWalletControllerOpenFailover gains a create-failover
case (preferred dead, fallback good -> walletOpen).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>