refactored broad range of the application, split files, modularized calendar and file views, centralized bottom sheets and clipboard handling, and implemented unit test coverage

lib/widget/async_actions/async_action_controller.dart

@@ -0,0 +1,63 @@
+part of '../async_action_button.dart';
+
+typedef AsyncActionCallback = Future<void> Function();
+typedef AsyncErrorBuilder = String Function(Object error);
+
+/// Wraps [action] with a try/catch that pops up an [InfoDialog] on failure
+/// (using [errorBuilder] or the default error mapper). Returns `true` on
+/// success, `false` on caught failure.
+Future<bool> runWithErrorDialog(
+  BuildContext context,
+  AsyncActionCallback action, {
+  AsyncErrorBuilder? errorBuilder,
+}) async {
+  try {
+    await action();
+    return true;
+  } catch (e) {
+    if (!context.mounted) return false;
+    final message = errorBuilder != null ? errorBuilder(e) : errorToUserMessage(e);
+    final details = errorToTechnicalDetails(e);
+    final body = details != null && details != message ? '$message\n\n$details' : message;
+    InfoDialog.show(context, body, copyable: true, title: 'Fehler');
+    return false;
+  }
+}
+
+/// Reusable busy/error state for the async-button family. Multiple buttons
+/// can share the same controller (e.g. a parent toolbar wanting to disable
+/// while any one child is running).
+class AsyncActionController extends ChangeNotifier {
+  bool _busy = false;
+  String? _error;
+
+  bool get busy => _busy;
+  String? get error => _error;
+
+  Future<bool> run(
+    AsyncActionCallback action, {
+    AsyncErrorBuilder? errorBuilder,
+  }) async {
+    if (_busy) return false;
+    _busy = true;
+    _error = null;
+    notifyListeners();
+    try {
+      await action();
+      _busy = false;
+      notifyListeners();
+      return true;
+    } catch (e) {
+      _busy = false;
+      _error = errorBuilder != null ? errorBuilder(e) : errorToUserMessage(e);
+      notifyListeners();
+      return false;
+    }
+  }
+
+  void clearError() {
+    if (_error == null) return;
+    _error = null;
+    notifyListeners();
+  }
+}