Add board service and repository, update routes and assets

- Introduced BoardService and BoardRepository for managing board-related data.
- Updated app routes to reflect the new board screen structure.
- Added new board-related assets to the asset manager.
- Refactored BoardScreen navigation to utilize the new provider structure.

lib/views/board/strings/board_strings.dart

@@ -0,0 +1,14 @@
+class BoardStrings {
+  BoardStrings._();
+
+  static const String boardTitle = 'My Board';
+  static const String toDo = 'To Do';
+  static const String inProgress = 'In Progress';
+  static const String done = 'Done';
+  static const String emptyListText = 'No tasks found';
+  static const String deadlineLabel = 'Deadline';
+  static const String readyLabel = 'Ready';
+  static const String incompleteLabel = 'Incomplete';
+  static String taskMovedMessage(String oldStatus, String newStatus) =>
+      'Task moved from $oldStatus to $newStatus';
+}