Create README_UA.md for Ukrainian localization

[VladimirGavrilyuk]

Ukrainian README (README_UA.md)

This PR adds a Ukrainian localization of the README file (README_UA.md).

What's included

• Full translation of all sections: Usage, Features, Supported Services, Plugin System, Installation (Windows/macOS/Linux), External Calls, Wayland Support, and Manual Compilation
• • Properly localized Ukrainian terminology (e.g., "застосунок" instead of "програма", correct use of Ukrainian grammar and punctuation)
• • Language switcher link added: [中文](./README.md) | [English](./README_EN.md) | [한글](./README_KR.md) | **Українська**
• • Consistent formatting with existing README_EN.md and README_KR.md

Notes

Ukrainian ISO 639-1 language code is uk, but to avoid confusion with the United Kingdom abbreviation (UK), the file follows the country code convention UA — which is consistent with how other projects handle Ukrainian localization.

The Weblate UI translation for Ukrainian (uk_UA) was also brought to 100% as part of this contribution.