feat(app): add background worker for provider health checks

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.

crates/owlen-tui/src/app/mod.rs

@@ -1,4 +1,5 @@
 mod generation;
+mod worker;
 
 pub mod messages;
 
@@ -51,6 +52,16 @@ impl App {
             active.abort();
         }
     }
+
+    /// Launch the background worker responsible for provider health checks.
+    pub fn spawn_background_worker(&self) -> JoinHandle<()> {
+        let manager = Arc::clone(&self.provider_manager);
+        let sender = self.message_tx.clone();
+
+        tokio::spawn(async move {
+            worker::background_worker(manager, sender).await;
+        })
+    }
 }
 
 struct ActiveGeneration {

crates/owlen-tui/src/app/worker.rs

@@ -0,0 +1,52 @@
+use std::sync::Arc;
+use std::time::Duration;
+
+use tokio::{sync::mpsc, time};
+
+use owlen_core::provider::ProviderManager;
+
+use super::AppMessage;
+
+const HEALTH_CHECK_INTERVAL: Duration = Duration::from_secs(30);
+
+/// Periodically refresh provider health and emit status updates into the app's
+/// message channel. Exits automatically once the receiver side of the channel
+/// is dropped.
+pub async fn background_worker(
+    provider_manager: Arc<ProviderManager>,
+    message_tx: mpsc::UnboundedSender<AppMessage>,
+) {
+    let mut interval = time::interval(HEALTH_CHECK_INTERVAL);
+    let mut last_statuses = provider_manager.provider_statuses().await;
+
+    loop {
+        interval.tick().await;
+
+        if message_tx.is_closed() {
+            break;
+        }
+
+        let statuses = provider_manager.refresh_health().await;
+
+        for (provider_id, status) in statuses {
+            let changed = match last_statuses.get(&provider_id) {
+                Some(previous) => previous != &status,
+                None => true,
+            };
+
+            last_statuses.insert(provider_id.clone(), status);
+
+            if changed
+                && message_tx
+                    .send(AppMessage::ProviderStatus {
+                        provider_id,
+                        status,
+                    })
+                    .is_err()
+            {
+                // Receiver dropped; terminate worker.
+                return;
+            }
+        }
+    }
+}