state recovery, polling optimizations, error rendering

widget states cached to SQLite, loaded on startup to seed DataProjection
so server restart preserves last-known data for reconnecting clients.

polling: first poll runs immediately, widget list cached per-task with
30s refresh, static text polled once inline instead of looping.

poll failures propagate WidgetError::SourceUnavailable to clients.
render engine prepends [offline] prefix in accent color, stale data
preserved below.

crates/application/src/data_projection.rs

@@ -19,6 +19,13 @@ impl DataProjection {
         Self::default()
     }
 
+    pub async fn seed(&self, states: Vec<(WidgetId, WidgetState)>) {
+        let mut current = self.current.lock().await;
+        for (id, state) in states {
+            current.insert(id, state);
+        }
+    }
+
     pub async fn get_state(&self, widget_id: WidgetId) -> Option<WidgetState> {
         self.current.lock().await.get(&widget_id).cloned()
     }