refactor(auth): replace TokenRecord with coreauth.Auth and migrate TokenStore to coreauth.Store

- Replaced `TokenRecord` with `coreauth.Auth` for centralized and consistent authentication data structures.
- Migrated `TokenStore` interface to `coreauth.Store` for alignment with core CLIProxy authentication.
- Updated related login methods, token persistence logic, and file storage handling to use the new `coreauth.Auth` model.

sdk/cliproxy/auth/manager.go

@@ -818,7 +818,8 @@ func (m *Manager) persist(ctx context.Context, auth *Auth) error {
 	if auth.Metadata == nil {
 		return nil
 	}
-	return m.store.SaveAuth(ctx, auth)
+	_, err := m.store.Save(ctx, auth)
+	return err
 }
 
 // StartAutoRefresh launches a background loop that evaluates auth freshness