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.

agent/src/collectors/mod.rs

@@ -16,9 +16,6 @@ pub use error::CollectorError;
 /// Base trait for all collectors with extreme efficiency requirements
 #[async_trait]
 pub trait Collector: Send + Sync {
-    /// Name of this collector
-    fn name(&self) -> &str;
-
     /// Collect all metrics this collector provides
     async fn collect(&self, status_tracker: &mut StatusTracker) -> Result<Vec<Metric>, CollectorError>;