Remove unused code and eliminate compiler warnings

- Remove unused fields from CommandStatus variants
- Clean up unused methods and unused collector fields
- Fix lifetime syntax warning in SystemWidget
- Delete unused cache module completely
- Remove redundant render methods from widgets

All agent and dashboard warnings eliminated while preserving
panel switching and scrolling functionality.

dashboard/src/ui/widgets/mod.rs

@@ -1,5 +1,4 @@
 use cm_dashboard_shared::Metric;
-use ratatui::{layout::Rect, Frame};
 
 pub mod backup;
 pub mod cpu;
@@ -16,6 +15,4 @@ pub trait Widget {
     /// Update widget with new metrics data
     fn update_from_metrics(&mut self, metrics: &[&Metric]);
 
-    /// Render the widget to a terminal frame
-    fn render(&mut self, frame: &mut Frame, area: Rect);
 }