custom login implementation, period-based timetable layout with overlap handling, enhanced error dialogs, and unified bottom sheets

lib/widget/file_viewer.dart

@@ -123,7 +123,7 @@ class _FileViewerState extends State<FileViewer> {
                     if (saved != null) InfoDialog.show(context, 'Datei gespeichert.');
                   } on Object catch (e) {
                     if (!context.mounted) return;
-                    InfoDialog.show(context, 'Speichern fehlgeschlagen: $e');
+                    InfoDialog.show(context, 'Speichern fehlgeschlagen: $e', copyable: true, title: 'Fehler');
                   }
                   break;
               }