added quotes export to file

frontend/lib/model/quote.dart

@@ -18,4 +18,9 @@ class Quote{
       body: json['body'],
     );
   }
+
+  @override 
+  String toString() {
+    return "$body - $author";
+  }
 }

frontend/lib/pages/list.dart

@@ -274,8 +274,15 @@ class ListPage extends StatelessWidget {
                   title: Text(Strings.exportSelectedQuotes),
                   trailing: Icon(Icons.import_export),
                   onTap: () {
-                    // TODO: trigger an os dialog FileSave
-                  },
+                    provider.exportQuotesToFile();
+                    Navigator.pop(context);
+                    ScaffoldMessenger.of(context).showSnackBar(
+                      SnackBar(
+                        content: Text(Strings.fileExportedSuccessfully),
+                        duration: const Duration(seconds: 3),
+                      ),
+                    );
+                  }
                 ),
               ],
             ),

frontend/lib/provider/quote_provider.dart

@@ -1,10 +1,12 @@
 // gets all quotes from the database and returns them in a list
 
+import 'package:path_provider/path_provider.dart';
 import 'package:flutter/material.dart';
 
 import 'package:frontend/model/quote.dart';
 import 'package:frontend/repository/quote_repository.dart';
 import 'dart:math';
+import 'dart:io';
 
 class QuoteProvider extends ChangeNotifier {
   List<Quote> _quotes = [];
@@ -149,4 +151,30 @@ class QuoteProvider extends ChangeNotifier {
     populateAuthors();
     notifyListeners();
   }
+
+
+  Future<Directory> _getSaveDirectory() async {
+    if (Platform.isWindows || Platform.isLinux || Platform.isMacOS) {
+      final path = Platform.isWindows
+          ? Platform.environment['USERPROFILE']
+          : Platform.environment['HOME'];
+
+      return Directory(path!);
+    }
+
+    // Mobile fallback
+    return await getApplicationDocumentsDirectory();
+  }
+
+  Future<void> exportQuotesToFile() async {
+    final dir = await _getSaveDirectory();
+
+    final datetime = DateTime.now().toUtc().toString()
+      .replaceAll(" ", "T")
+      .replaceAll(":", "-")
+      .replaceAll(RegExp(r"\..*"), "");
+
+    final file = File('${dir.path}/hlasky_$datetime.txt');
+    await file.writeAsString("${filteredQuotes.join("\n")}\n");
+  }
 }

frontend/lib/values/strings.dart

@@ -22,6 +22,7 @@ class Strings {
   static const String flipFlashcard = "Otočit flashkartu";
   static const String nextFlashcard = "Další flashkarta";
 
+  static const String fileExportedSuccessfully = "Soubor byl úspěšně vyexportován.";
   static const String noUndo = "Tuto akci nelze odčinit.";
   static const String filterQuery = "Filtrovací požadavek";
   static const String allQuotesCount = "Celkový počet hlášek";