The Create Folder action ignored the sidebar selection and always
wrote to the vault root. Now it threads the selected folder as
parent_path to the backend, and expands the parent in the tree so
the new child is visible without re-clicking.
Fixes: https://github.com/refactoringhq/tolaria/issues/728
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>