Show refreshing status during library scan

- Add is_refreshing flag to AppState
- Display 'Refreshing library...' in status panel during scan
- Note: scan is currently blocking, message may be brief
- Infrastructure ready for future async scanning

src/main.rs

@@ -178,12 +178,14 @@ async fn handle_key_event(state: &mut AppState, player: &mut player::Player, key
             }
         }
         KeyCode::Char('r') => {
+            state.is_refreshing = true;
             tracing::info!("Rescanning...");
             let cache_dir = cache::get_cache_dir()?;
             let new_cache = scanner::scan_paths(&state.config.scan_paths.paths)?;
             new_cache.save(&cache_dir)?;
             state.cache = new_cache;
             state.refresh_flattened_items();
+            state.is_refreshing = false;
             tracing::info!("Rescan complete");
         }
         _ => {}