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/backup.rs

@@ -107,9 +107,6 @@ impl BackupCollector {
 
 #[async_trait]
 impl Collector for BackupCollector {
-    fn name(&self) -> &str {
-        "backup"
-    }
 
     async fn collect(&self, _status_tracker: &mut StatusTracker) -> Result<Vec<Metric>, CollectorError> {
         let backup_status_option = self.read_backup_status().await?;