fix(sdk): synchronize theme preference across containers

[Huxpro]

Summary

• persist the app theme preference in the native Sparkling SDK on Android and iOS
• inject preferredTheme into newly created containers and broadcast changes to active containers
• keep force_theme_style as the highest-priority per-page override
• update the playground to use the native preference API and add focused frontend/native tests

Validation

• playground theme preference tests: 3 passed
• playground production build: passed
• Android ThemePreferenceTest: 6 passed
• Android SG1 Lynx Sandbox: theme switch, new-container inheritance, and relaunch persistence verified
• iOS: new Swift tests compile; Simulator manual validation verified theme switch, new-container inheritance, and relaunch persistence
• note: local xcodebuild test execution is blocked by an existing Xcode/CoreSimulator empty build-number issue that shuts down the destination

Fixes #56