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/Constants/AppGroup.swift

@@ -23,6 +23,15 @@ public enum AppGroup {
         ) != nil
     }()
 
+    /// On-disk container path (or `"nil"`) for diagnostics. When this reads
+    /// `nil` in a process, that process cannot share App Group state — the
+    /// `CFPrefsPlistSource … Container: (null)` console warning comes from here.
+    public static var containerPathForDiagnostics: String {
+        FileManager.default.containerURL(
+            forSecurityApplicationGroupIdentifier: identifier
+        )?.path ?? "nil"
+    }
+
     /// Shared UserDefaults when the App Group suite is available; `nil` otherwise.
     ///
     /// Prefer this in Release builds and in the keyboard extension so callers