feat: iCloud settings sync and cold-start return redesign

- Add iCloud key-value settings sync (engine/language/polish/Flow prefs);
  API keys stay on-device. New "Sync settings via iCloud" toggle.
- Redesign cold-start handoff: bottom-bar left-to-right swipe guidance,
  auto-dismiss on app switch, tap-anywhere to close, retained return link.
- Harden keyboard->app handoff with host-disconnected hint.
- Include prior Unreleased ASR fixes (route-change crash, fallback warning,
  multi-utterance recognition, local ASR diagnostics).

Release 0.5.0 (build 18).

OSGKeyboardExt/Services/KeyboardConfigSync.swift

@@ -72,7 +72,10 @@ final class KeyboardConfigSync {
 
     func syncOnboardingStateFromAppGroup() {
         let store = AppGroupStore()
-        state.hasCompletedOnboarding = store.hasCompletedOnboarding
+        // Fall back to the reboot-durable Keychain marker so a device restart
+        // does not resurrect the in-keyboard onboarding overlay when the App
+        // Group value transiently reads empty.
+        state.hasCompletedOnboarding = store.hasCompletedOnboarding || Keychain.hasCompletedOnboarding()
         state.onboardingPage = store.onboardingPage
     }