That client_app folder has a .git
in it, which makes client_app a nested git repository for its parent main repository.
A nested Git repository is treated as a gitlink
160000: A gitlink, SHA-1 of the object refers to a commit in another repository. Git links can only be specified by SHA or through a commit mark.
They are used to implement submodules.
Unless you main repository has a .gitmodules
file, you cannot directly stage content in client_app.
Or, as commented, you would need to delete its .git/
subfolder in order for the main repository to see client_app as a regular folder.