Implement complete keyboard navigation and UI enhancement

Phase 1 - Panel Navigation:
- Add PanelType enum and panel focus state management
- Implement Shift+Tab cycling between panels (System → Services → Backup → Network)
- Add visual focus indicators with blue borders for focused panels
- Preserve existing Tab behavior for host switching

Phase 2 - Dynamic Statusbar:
- Add bottom statusbar with context-aware shortcuts
- Display different shortcuts based on focused panel
- Global shortcuts: Tab, Shift+Tab, Up/Down arrows, Q
- Panel-specific shortcuts: R (Rebuild), Space/R (Services), B (Backup), N (Network)

Phase 3 - Scrolling Support:
- Add scroll state management per host and panel type
- Implement Up/Down arrow key scrolling within focused panels
- Smart scrolling that activates only when content exceeds panel height
- Scroll bounds checking to prevent over-scrolling

Complete keyboard navigation experience with visual feedback and contextual help.

dashboard/src/ui/widgets/system.rs

@@ -399,6 +399,13 @@ impl Widget for SystemWidget {
     }
 
     fn render(&mut self, frame: &mut Frame, area: Rect) {
+        self.render_with_scroll(frame, area, 0);
+    }
+}
+
+impl SystemWidget {
+    /// Render with scroll offset support
+    pub fn render_with_scroll(&mut self, frame: &mut Frame, area: Rect, scroll_offset: usize) {
         let mut lines = Vec::new();
 
         // NixOS section
@@ -509,7 +516,28 @@ impl Widget for SystemWidget {
             }
         }
 
-        let paragraph = Paragraph::new(Text::from(lines));
-        frame.render_widget(paragraph, area);
+        // Apply scroll offset
+        let total_lines = lines.len();
+        let available_height = area.height as usize;
+        
+        if total_lines > available_height {
+            // Content is larger than area, apply scrolling
+            let max_scroll = total_lines.saturating_sub(available_height);
+            let effective_scroll = scroll_offset.min(max_scroll);
+            
+            // Take only the visible portion after scrolling
+            let visible_lines: Vec<Line> = lines
+                .into_iter()
+                .skip(effective_scroll)
+                .take(available_height)
+                .collect();
+                
+            let paragraph = Paragraph::new(Text::from(visible_lines));
+            frame.render_widget(paragraph, area);
+        } else {
+            // All content fits, render normally
+            let paragraph = Paragraph::new(Text::from(lines));
+            frame.render_widget(paragraph, area);
+        }
     }
 }