Add HarmonyOS (鸿蒙) SDK support

[telsav]

flutter-skill supports 8 platforms. HarmonyOS (Huawei) is growing fast in China. Adding an SDK for HarmonyOS/ArkTS would make flutter-skill the first AI testing tool supporting 9 platforms including HarmonyOS.

What's needed:

• A bridge SDK in ArkTS/JS that implements the flutter-skill bridge protocol
• WebSocket server on port 18118
• Implement: screenshot, tap, enter_text, scroll, inspect, go_back

Reference: See sdks/electron/ for a JavaScript-based SDK example.

Good first issue for anyone familiar with HarmonyOS development.