Adds SyncSetupPlugin: a three-field (URL / Username / Password) modal
that handles both login and register flows via an async task on
AsyncComputeTaskPool wrapped in a Tokio single-thread runtime (same
pattern as the existing sync push/pull). On success, tokens are stored
to the OS keychain / Android Keystore and SyncProviderResource is
hot-swapped so subsequent pull/push use the new credentials immediately.
Settings sync section now shows Connect (when Local) or Sync Now +
Disconnect + username label (when SolitaireServer). SyncAuthResultEvent
stub registered for future re-auth prompt wiring.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
funman300
432061c3ec