Introduce a `worker` module with `background_worker` that periodically refreshes provider health and emits status updates via the app's message channel. Add `spawn_background_worker` method to `App` for launching the worker as a Tokio task.
Introduce a `worker` module with `background_worker` that periodically refreshes provider health and emits status updates via the app's message channel. Add `spawn_background_worker` method to `App` for launching the worker as a Tokio task.