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).

OSGKeyboardTests/FakeUbiquitousKeyValueStore.swift

@@ -0,0 +1,37 @@
+// FakeUbiquitousKeyValueStore.swift
+// OSGKeyboardTests
+//
+// In-memory KVS fake for hermetic iCloud sync tests.
+
+import Foundation
+@testable import OSGKeyboardShared
+
+final class FakeUbiquitousKeyValueStore: UbiquitousKeyValueStoreing, @unchecked Sendable {
+    private var storage: [String: Any] = [:]
+
+    func data(forKey key: String) -> Data? {
+        storage[key] as? Data
+    }
+
+    func set(_ value: Data?, forKey key: String) {
+        if let value {
+            storage[key] = value
+        } else {
+            storage.removeValue(forKey: key)
+        }
+    }
+
+    func object(forKey key: String) -> Any? {
+        storage[key]
+    }
+
+    func set(_ value: Any?, forKey key: String) {
+        if let value {
+            storage[key] = value
+        } else {
+            storage.removeValue(forKey: key)
+        }
+    }
+
+    func synchronize() -> Bool { true }
+}