Previously, the app only sent an HTTP shutdown request to the Python
sidecar with no timeout and no fallback. If the request failed, the
sidecar process became orphaned, causing memory leaks.
- Add 3-second timeout to the HTTP shutdown request
- Add fallback to force-kill the sidecar by PID (taskkill /F /T on
Windows, kill -9 on Unix) after HTTP shutdown attempt
- Store child PID in AppState for use in both window close handler
and Tauri command shutdown
Fixes#944
zanllp