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/adapters/config-memory/src/lib.rs

@@ -1,6 +1,6 @@
 use domain::{
     ConfigRepository, DataSource, DataSourceId, Layout, LayoutPreset, LayoutPresetId, ThemeConfig,
-    User, WidgetConfig, WidgetId,
+    User, WidgetConfig, WidgetId, WidgetState,
 };
 use std::collections::HashMap;
 use std::sync::RwLock;
@@ -203,4 +203,15 @@ impl ConfigRepository for MemoryConfigStore {
             .map_err(|_| MemoryConfigError::LockPoisoned)?;
         Ok(guard.len() as u32)
     }
+
+    async fn save_widget_states(
+        &self,
+        _states: &[(WidgetId, WidgetState)],
+    ) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn load_widget_states(&self) -> Result<Vec<(WidgetId, WidgetState)>, Self::Error> {
+        Ok(vec![])
+    }
 }