Get Note Translations

Return translated note node descriptions for the current locale.

Returns a mapping of node_id → translated markdown text. Only nodes with a matching translation key are included; nodes without translations are omitted so the caller can leave them unchanged.

A missing or inaccessible flow yields 404 (via AuthorizedReadFlow), consistent with GET /flows/{id}; the sole frontend caller (NoteNode) treats that as "no translations" and renders the original text.