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/theme.rs

@@ -226,10 +226,6 @@ impl Layout {
     /// System vs backup split (equal)
     pub const SYSTEM_PANEL_HEIGHT: u16 = 50;
     pub const BACKUP_PANEL_HEIGHT: u16 = 50;
-    /// System panel CPU section height
-    pub const CPU_SECTION_HEIGHT: u16 = 2;
-    /// System panel memory section height  
-    pub const MEMORY_SECTION_HEIGHT: u16 = 3;
 }
 
 /// Typography system