Clean up UI code and improve agent hash display

- Remove unused imports and debug logging
- Change agent display from 'Agent Hash: full' to 'Agent: short8'
- Fix unused variable warnings

dashboard/src/ui/mod.rs

@@ -406,7 +406,7 @@ impl TuiApp {
         }
     }
 
-    fn render_system_panel(&mut self, frame: &mut Frame, area: Rect, metric_store: &MetricStore) {
+    fn render_system_panel(&mut self, frame: &mut Frame, area: Rect, _metric_store: &MetricStore) {
         let system_block = Components::widget_block("system");
         let inner_area = system_block.inner(area);
         frame.render_widget(system_block, area);