refactor: Integrate PlatformPaths for configuration directory management

- Replaced direct calls to GetConfigDirectory with PlatformPaths::GetConfigDirectory across multiple files to standardize configuration directory access.
- Updated RecentFilesManager, EditorManager, and various agent components to handle potential errors when retrieving the configuration directory.
- Enhanced file loading functions to utilize the new LoadFileFromConfigDir method for improved clarity and error handling.
- Introduced new methods in file_util.h for better file management practices, leveraging std::filesystem for cross-platform consistency.

src/app/editor/ui/editor_selection_dialog.cc

@@ -344,7 +344,7 @@ void EditorSelectionDialog::MarkRecentlyUsed(EditorType type) {
 
 void EditorSelectionDialog::LoadRecentEditors() {
   try {
-    auto data = util::LoadConfigFile("recent_editors.txt");
+    auto data = util::LoadFileFromConfigDir("recent_editors.txt");
     if (!data.empty()) {
       std::istringstream ss(data);
       std::string line;