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).

OSGKeyboardShared/Services/AppGroupStore.swift

@@ -57,6 +57,7 @@ public struct AppGroupStore: @unchecked Sendable {
     public var polishModeForPipeline: PolishingService.PolishMode { configuration.polishModeForPipeline }
     public var polishProviderIdOverride: String? { configuration.polishProviderIdOverride }
     public var isCloudAPIKeyMissingForVoiceInput: Bool { configuration.isCloudAPIKeyMissingForVoiceInput }
+    public var localASRCustomLanguageModelEnabled: Bool { configuration.localASRCustomLanguageModelEnabled }
 
     /// Whether the keyboard top-bar translation chip should render.
     public var isTranslationChipVisible: Bool { true }
@@ -112,6 +113,10 @@ public struct AppGroupStore: @unchecked Sendable {
         mutateConfiguration { $0.polishIntensity = intensity }
     }
 
+    public func setLocalASRCustomLanguageModelEnabled(_ enabled: Bool) {
+        mutateConfiguration { $0.localASRCustomLanguageModelEnabled = enabled }
+    }
+
     public var hasCompletedOnboarding: Bool {
         get { configuration.hasCompletedOnboarding }
         set { setHasCompletedOnboarding(newValue) }
@@ -129,6 +134,8 @@ public struct AppGroupStore: @unchecked Sendable {
                 config.onboardingPage = 0
             }
         }
+        // Mirror to the reboot-durable Keychain marker (keyboard-side completion).
+        Keychain.setOnboardingCompleted(completed)
     }
 
     public func setOnboardingPage(_ page: Int) {
@@ -167,6 +174,22 @@ public struct AppGroupStore: @unchecked Sendable {
         mutateConfiguration { $0.personalDictionaryICloudSyncEnabled = enabled }
     }
 
+    public var settingsICloudSyncEnabled: Bool {
+        get { configuration.settingsICloudSyncEnabled }
+        set { setSettingsICloudSyncEnabled(newValue) }
+    }
+
+    public func setSettingsICloudSyncEnabled(_ enabled: Bool) {
+        mutateConfiguration { $0.settingsICloudSyncEnabled = enabled }
+    }
+
+    /// Timestamp of the last settings blob applied from iCloud KVS.
+    public var settingsCloudUpdatedAt: Date? {
+        let raw = defaults.double(forKey: AppGroupConfiguration.Keys.settingsCloudUpdatedAt)
+        guard raw > 0 else { return nil }
+        return Date(timeIntervalSince1970: raw)
+    }
+
     // MARK: - Client
 
     public func makeClient() -> LLMClient {