0.3.0

Add settings panel and updater integration

Introduce a Settings panel and updater flow: add a SettingsPanel React component, styles, and a settings icon; update TitleBar to show a settings button and update badge; wire App to open the panel and auto-check updates (via plugin-store). Add src/utils/updater.js as a thin wrapper around @tauri-apps/plugin-updater to check, download, and install updates. Initialize tauri-plugin-store in the Rust main and register the tauri-plugin-updater (desktop only); expose updater/store capabilities in src-tauri/capabilities/default.json. Also add TAURI_SIGNING_PRIVATE_KEY to the GitHub Actions workflow environment for signing. UI/cosmetic adjustments include importing the new styles into main.scss.