Update backup widget layout and fix system widget Single label

Backup widget:
- Restructure to match new layout specification
- Add section headers: Latest backup, Disk, Repos
- Show timestamp with status icon and duration as sub-item
- Display disk info with product name, S/N, and usage in tree structure
- List repositories with archive count and size
- Remove old render methods and unused imports

System widget:
- Hide (Single) storage type label for cleaner display

dashboard/src/ui/widgets/system.rs

@@ -254,7 +254,11 @@ impl SystemWidget {
                 _ => "—% —GB/—GB".to_string(),
             };
             
-            let pool_label = format!("{} ({}):", pool.mount_point, pool.pool_type);
+            let pool_label = if pool.pool_type.to_lowercase() == "single" {
+                format!("{}:", pool.mount_point)
+            } else {
+                format!("{} ({}):", pool.mount_point, pool.pool_type)
+            };
             let pool_spans = StatusIcons::create_status_spans(
                 pool.status.clone(),
                 &pool_label