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/client-desktop/src/main.rs

@@ -2,7 +2,7 @@ use client_application::ClientApp;
 use client_domain::NetworkPort;
 use client_domain::{BoundingBox, DisplayPort, FontMetrics, RenderEngine, ThemeConfig};
 use display_terminal::TerminalDisplay;
-use domain::DisplayHint;
+use domain::{DisplayHint, WidgetError};
 use protocol::decode_server_message;
 use std::sync::mpsc;
 use std::thread;
@@ -85,7 +85,10 @@ fn main() {
                             .map(|kv| (kv.key.clone(), kv.value.clone().into()))
                             .collect();
 
-                        let draw_cmds = engine.render_widget(&hint, &data, cmd.bounds, 0);
+                        let error: Option<WidgetError> =
+                            cmd.state.error.as_ref().map(|e| e.clone().into());
+                        let draw_cmds =
+                            engine.render_widget(&hint, &data, cmd.bounds, 0, error.as_ref());
                         for dc in &draw_cmds {
                             display
                                 .draw_text_span(&dc.text, dc.x, dc.y, dc.color, dc.font)