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/FlowSessionKeys.swift

@@ -26,9 +26,16 @@ public enum FlowSessionKeys {
     /// Wall-clock timestamp of the last utterance completion or session start.
     public static let lastActivityAt = "flow.lastActivityAt"
 
-    /// Heartbeat older than this while the host is foreground → likely killed.
+    /// Heartbeat older than this → host is not actively reachable for recording.
     public static let heartbeatStaleInterval: TimeInterval = 3
 
+    /// Session flag still set but heartbeat older than this → host process is
+    /// dead (force-quit, reboot). Keyboard / host should clear persisted state.
+    public static let heartbeatZombieInterval: TimeInterval = 60
+
+    /// After mic stop, fail fast when the host heartbeat is gone longer than this.
+    public static let keyboardHostDisconnectFailFast: TimeInterval = 15
+
     /// Legacy fixed session length — prefer `FlowSessionPolicy.sessionDuration()`.
     public static let defaultSessionDuration: TimeInterval = 480