return external_id with directory response in tree

Signed-off-by: phernandez <paul@basicmachines.co>

Author: phernandez

src/basic_memory/services/directory_service.py

@@ -252,6 +252,7 @@ def _build_directory_tree_from_entities(
                 type="file",
                 title=file.title,
                 permalink=file.permalink,
+                external_id=file.external_id,  # UUID for v2 API
                 entity_id=file.id,
                 entity_type=file.entity_type,
                 content_type=file.content_type,