While a task for an app is in progress, disable the UI elements which would trigger a new task.

[stmh]

Currently you can run multiple tasks for the same app at the same time, this should be prevented. On the other hand we need the possibility to cancel a running task to enable the UI again. The concurrent task prevention should be handled ideally by the backend

[stmh]

📋 Bead created: scotty-2ffb

This issue is now being tracked in the beads system. The implementation should:

1. Backend: Track active tasks per app and reject concurrent task requests
2. Frontend: Disable UI elements during task execution
3. Consider: Task cancellation functionality to unblock the UI