Change tree symbols to use secondary text color

Update all tree symbols (└─, ├─) in system and backup widgets to use
Typography::secondary() style instead of raw text for consistent
text coloring throughout the interface.

dashboard/src/ui/widgets/system.rs

@@ -286,7 +286,7 @@ impl SystemWidget {
 
                 let mut drive_spans = vec![
                     Span::raw("  "),
-                    Span::raw(tree_symbol),
+                    Span::styled(tree_symbol, Typography::secondary()),
                     Span::raw(" "),
                 ];
                 drive_spans.extend(StatusIcons::create_status_spans(drive.status.clone(), &drive_text));
@@ -298,7 +298,7 @@ impl SystemWidget {
                 let tree_symbol = "└─";
                 let mut usage_spans = vec![
                     Span::raw("  "),
-                    Span::raw(tree_symbol),
+                    Span::styled(tree_symbol, Typography::secondary()),
                     Span::raw(" "),
                 ];
                 usage_spans.extend(StatusIcons::create_status_spans(pool.status.clone(), &usage_text));
@@ -435,7 +435,7 @@ impl Widget for SystemWidget {
         
         let freq_text = self.format_cpu_frequency();
         lines.push(Line::from(vec![
-            Span::raw("  └─ "),
+            Span::styled("  └─ ", Typography::secondary()),
             Span::styled(format!("Freq: {}", freq_text), Typography::secondary())
         ]));
 
@@ -453,7 +453,7 @@ impl Widget for SystemWidget {
 
         let tmp_text = self.format_tmp_usage();
         let mut tmp_spans = vec![
-            Span::raw("  └─ "),
+            Span::styled("  └─ ", Typography::secondary()),
         ];
         tmp_spans.extend(StatusIcons::create_status_spans(
             self.memory_status.clone(),