refactor(auth): replace FileStore with FileTokenStore for unified token persistence

- Removed `FileStore` in favor of the new `FileTokenStore`.
- Centralized auth JSON handling and token operations through `FileTokenStore`.
- Updated all components to utilize `FileTokenStore` for consistent storage operations.
- Introduced `SetBaseDir` and directory locking mechanisms for flexible configurations.
- Enhanced metadata management, including path resolution and deep JSON comparisons.

sdk/cliproxy/auth/manager.go

@@ -817,7 +817,7 @@ func (m *Manager) persist(ctx context.Context, auth *Auth) error {
 	if auth.Metadata == nil {
 		return nil
 	}
-	return m.store.Save(ctx, auth)
+	return m.store.SaveAuth(ctx, auth)
 }
 
 // StartAutoRefresh launches a background loop that evaluates auth freshness