refactor(ui): reorganize collection menus and sorting

- move MainMenu to the root ui package
- add CurrentCollectionMenu for current collection operations
- move sorting components under collection/sorting
- add CollectionFileSaveWindow for saving collections to file
- update imports and menu delegation

app/src/main/java/ru/project/ui/collection/CurrentCollectionMenu.java

@@ -0,0 +1,64 @@
+package ru.project.ui.collection;
+
+import com.googlecode.lanterna.gui2.ActionListBox;
+import com.googlecode.lanterna.gui2.WindowBasedTextGUI;
+import ru.project.model.AppState;
+import ru.project.ui.base.BaseModalWindow;
+import ru.project.ui.collection.sorting.SortCollectionMenu;
+import ru.project.ui.common.CollectionDisplayWindow;
+import ru.project.ui.common.CollectionFileSaveWindow;
+import ru.project.ui.common.MessageWindow;
+
+public class CurrentCollectionMenu extends BaseModalWindow {
+
+  private final AppState state;
+
+  private final SortCollectionMenu sortCollectionMenu;
+
+  public CurrentCollectionMenu(WindowBasedTextGUI gui, AppState state) {
+
+    super("Меню текущей коллекции", gui);
+
+    this.state = state;
+
+    this.sortCollectionMenu = new SortCollectionMenu(gui, state);
+
+    ActionListBox menu = new ActionListBox();
+
+    menu.addItem("Показать коллекцию", this::showCurrentCollection);
+
+    menu.addItem("Сохранить коллекцию в файл", this::saveCurrentCollection);
+
+    menu.addItem("Сортировать коллекцию", sortCollectionMenu::showModal);
+
+    menu.addItem("Поиск элемента в коллекции", this::searchCollection);
+
+    menu.addItem("Подсчёт количества вхождений элемента", this::countOccurrences);
+
+    menu.addItem("Выйти", this::close);
+
+    setComponent(menu);
+  }
+
+  private void showCurrentCollection() {
+    CollectionDisplayWindow window = new CollectionDisplayWindow(gui, state.getMainCollection());
+
+    window.showModal();
+  }
+
+  private void saveCurrentCollection() {
+    CollectionFileSaveWindow window = new CollectionFileSaveWindow(gui, state.getMainCollection());
+
+    window.showModal();
+  }
+
+  private void searchCollection() {
+    // TODO
+    MessageWindow.showModal(gui, "Не реализовано.");
+  }
+
+  private void countOccurrences() {
+    // TODO
+    MessageWindow.showModal(gui, "Не реализовано.");
+  }
+}