feat(settings): add configurable close-window behavior

[zaixiaziyang]

Summary

• add a desktop-only close-window preference for minimizing to the system tray or quitting the application
• persist the preference locally and synchronize it with the Tauri close-event handler
• reuse the existing terminal-session exit confirmation path when quitting
• preserve minimize-to-tray as the default for backward compatibility

Validation

• node --test test/settings/normalization.test.mjs (37 passed)
• TypeScript typecheck
• Vite production build
• cargo check --tests
• targeted Biome and rustfmt checks
• git diff --check