feat(ui): implement Slint-based UI for champion runes

* Add Slint UI components for source selection and rune display.
* Create settings management for user preferences.
* Integrate WebSocket client for League Client communication.
* Implement background tasks for fetching sources and monitoring LCU.
* Add build script for Slint compilation.
* Refactor main application logic to support new UI structure.

Author: cangzhang