feat: Enhance AgentChatWidget with system prompt management and project settings

- Updated system prompt loading functionality to support both version 1 and version 2 prompts, allowing users to load built-in prompts directly.
- Implemented custom system prompt loading and saving capabilities, enabling users to manage their prompts more effectively.
- Added methods to load and save agent settings from/to project files, including AI provider configurations and custom prompts.
- Improved user feedback with toast notifications for successful and failed operations related to system prompts and settings.

src/app/editor/editor_manager.cc

@@ -514,7 +514,7 @@ void EditorManager::Initialize(const std::string& filename) {
             context_.shortcut_manager.GetKeys("Open"),
             context_.shortcut_manager.GetCallback("Open")},
            {absl::StrCat(ICON_MD_HISTORY, " Open Recent"), "", []() {},
-            []() { return !manager.GetRecentFiles().empty(); }, recent_files},
+            [&manager]() { return !manager.GetRecentFiles().empty(); }, recent_files},
            {absl::StrCat(ICON_MD_FILE_DOWNLOAD, " Save"),
             context_.shortcut_manager.GetKeys("Save"),
             context_.shortcut_manager.GetCallback("Save")},