Clock Air APP MVP

Goal

Upgrade the built-in world-clock Air APP into a focused clock suite while keeping desktop clock widgets as lightweight launch entry points.

Keep the existing Air APP id world-clock for Launcher lifecycle compatibility.
Use one global Clock Air APP instance for every clock widget entry point.
Provide four tabs: World Clock, Stopwatch, Timer, and Settings.
Store Clock Air APP settings independently from desktop widget settings at AirApps/Clock/settings.json.
Follow the host language setting and provide localized text for zh-CN, en-US, ja-JP, and ko-KR.

world-clock opens as a standard resizable FluentAvalonia window.
The default window size is approximately 780x560, with a minimum of 680x480.
World Clock shows local time and a configurable city list.
Default city list is Beijing, London, Sydney, and New York.
Users can add, remove, and reorder city entries during the Air APP session; the list persists across restarts.
Stopwatch supports start, pause, resume, lap, and reset; laps are kept in the current window session, up to 50 entries.
Timer supports fixed presets, a custom minute duration, start, pause, resume, reset, and a completed state.
Closing the Clock Air APP stops stopwatch and timer activity.
Minimizing the window keeps stopwatch and timer activity running.
Timer completion can activate the Clock Air APP window when the setting is enabled.