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/info_dialog.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
-import 'package:flutter/services.dart';
+
+import '../utils/clipboard_helper.dart';
 
 class InfoDialog {
   /// Shows a single-text dialog. When [copyable] is true (default for error
@@ -26,16 +27,7 @@ class InfoDialog {
           actions: [
             if (copyable)
               TextButton.icon(
-                onPressed: () async {
-                  await Clipboard.setData(ClipboardData(text: info));
-                  if (!dialogContext.mounted) return;
-                  ScaffoldMessenger.of(dialogContext).showSnackBar(
-                    const SnackBar(
-                      content: Text('In Zwischenablage kopiert'),
-                      duration: Duration(seconds: 2),
-                    ),
-                  );
-                },
+                onPressed: () => copyToClipboard(dialogContext, info),
                 icon: const Icon(Icons.copy_outlined, size: 18),
                 label: const Text('Kopieren'),
               ),