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/nixos.rs

@@ -12,12 +12,11 @@ use crate::config::NixOSConfig;
 /// - NixOS version and build information
 /// - Currently active/logged in users
 pub struct NixOSCollector {
-    config: NixOSConfig,
 }
 
 impl NixOSCollector {
-    pub fn new(config: NixOSConfig) -> Self {
-        Self { config }
+    pub fn new(_config: NixOSConfig) -> Self {
+        Self {}
     }
 
     /// Get NixOS build information
@@ -116,9 +115,6 @@ impl NixOSCollector {
 
 #[async_trait]
 impl Collector for NixOSCollector {
-    fn name(&self) -> &str {
-        "nixos"
-    }
 
     async fn collect(&self, _status_tracker: &mut StatusTracker) -> Result<Vec<Metric>, CollectorError> {
         debug!("Collecting NixOS system information");