implemented message forwarding and direct chat creation from group members, and added specialized share picker for forwarded content

lib/view/pages/share_intent/share_chat_picker.dart

@@ -7,6 +7,8 @@ import 'package:persistent_bottom_nav_bar_v2/persistent_bottom_nav_bar_v2.dart';
 
 import '../../../api/errors/error_mapper.dart';
 import '../../../api/marianumcloud/talk/room/get_room_response.dart';
+import '../../../api/marianumcloud/talk/send_message/send_message.dart';
+import '../../../api/marianumcloud/talk/send_message/send_message_params.dart';
 import '../../../api/marianumcloud/talk/share_files_to_chat.dart';
 import '../../../api/marianumcloud/webdav/webdav_api.dart';
 import '../../../routing/app_routes.dart';
@@ -47,6 +49,23 @@ class ShareChatPicker extends StatelessWidget {
         onPicked: (ctx, room) => _internalShareFlow(ctx, room, file),
       );
 
+  /// Forward an existing Talk message (text and/or already-uploaded file
+  /// attachment) into another chat. The attachment is re-shared via the same
+  /// FileSharingApi path used for [forInternalShare]; plain text is posted
+  /// with [SendMessage].
+  factory ShareChatPicker.forMessageForward({
+    String? text,
+    RemoteFileRef? file,
+  }) {
+    assert(
+      text != null || file != null,
+      'forMessageForward requires either text or file',
+    );
+    return ShareChatPicker._(
+      onPicked: (ctx, room) => _forwardMessageFlow(ctx, room, text, file),
+    );
+  }
+
   @override
   Widget build(BuildContext context) {
     final talkSettings = context.watch<SettingsCubit>().val().talkSettings;
@@ -217,6 +236,39 @@ Future<void> _internalShareFlow(
   _finishWithChat(context, room);
 }
 
+Future<void> _forwardMessageFlow(
+  BuildContext context,
+  GetRoomResponseObject room,
+  String? text,
+  RemoteFileRef? file,
+) async {
+  unawaited(_showBlockingSpinner(context));
+  try {
+    if (file != null) {
+      await shareFilesToChat(
+        token: room.token,
+        remoteFilePaths: [file.path],
+      );
+    }
+    if (text != null && text.isNotEmpty) {
+      await SendMessage(room.token, SendMessageParams(text)).run();
+    }
+  } catch (e) {
+    if (context.mounted) Navigator.of(context).pop();
+    if (context.mounted) {
+      InfoDialog.show(
+        context,
+        errorToUserMessage(e),
+        title: 'Fehler',
+        copyable: true,
+      );
+    }
+    return;
+  }
+  if (!context.mounted) return;
+  _finishWithChat(context, room);
+}
+
 /// Modal progress overlay shown during share-API roundtrips. The dialog is
 /// popped together with the picker by the subsequent popUntil(isFirst).
 Future<void> _showBlockingSpinner(BuildContext context) => showDialog<void>(