Add disk wear monitoring and fix storage overflow display

- Add disk wear percentage collection from SMART data in backup script
- Add backup_disk_wear_percent metric to backup collector with thresholds
- Display wear percentage in backup widget disk section
- Fix storage section overflow handling to use consistent "X more below" logic
- Update maintenance mode to return pending status instead of unknown

dashboard/src/ui/mod.rs

@@ -678,7 +678,7 @@ impl TuiApp {
                 Status::Pending => ok_count += 1, // Treat pending as OK for aggregation
                 Status::Ok => ok_count += 1,
                 Status::Inactive => ok_count += 1, // Treat inactive as OK for aggregation
-                Status::Unknown => {}, // Ignore unknown for aggregation
+                Status::Unknown => ok_count += 1, // Treat unknown as OK for aggregation
                 Status::Offline => {}, // Ignore offline for aggregation
             }
         }