Remove 'Repo' prefix from backup header display

Simplify backup section header by removing the 'Repo' prefix and
displaying only the timestamp with status icon. Repository details
are still shown as sub-items below the timestamp.

dashboard/src/ui/widgets/system.rs

@@ -544,9 +544,8 @@ impl SystemWidget {
             "unknown".to_string()
         };
 
-        // Header: "Repo <complete timestamp>"
-        let repo_text = format!("Repo {}", time_display);
-        let repo_spans = StatusIcons::create_status_spans(self.backup_status, &repo_text);
+        // Header: just the timestamp
+        let repo_spans = StatusIcons::create_status_spans(self.backup_status, &time_display);
         lines.push(Line::from(repo_spans));
 
         // List all repositories with archive count and size