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/cpu.rs

@@ -15,7 +15,6 @@ use crate::config::CpuConfig;
 /// - No process spawning
 /// - <0.1ms collection time target
 pub struct CpuCollector {
-    name: String,
     load_thresholds: HysteresisThresholds,
     temperature_thresholds: HysteresisThresholds,
 }
@@ -34,7 +33,6 @@ impl CpuCollector {
         );
         
         Self {
-            name: "cpu".to_string(),
             load_thresholds,
             temperature_thresholds,
         }
@@ -197,9 +195,6 @@ impl CpuCollector {
 
 #[async_trait]
 impl Collector for CpuCollector {
-    fn name(&self) -> &str {
-        &self.name
-    }
 
     async fn collect(&self, status_tracker: &mut StatusTracker) -> Result<Vec<Metric>, CollectorError> {
         debug!("Collecting CPU metrics");