Header should not be visible when logged out.

**Describe the bug**
Currently, the header is shown when the user is logged out, which contains the `logout` button itself. This is quite confusing to the users.

**To Reproduce**
Simply start the project and you can see the header without login.

**Expected behavior**
The header should be hidden when logged out.

**Screenshots**
N/A

**Environment (please complete the following information):**
- OS: [e.g. iOS]
- Version [e.g. 22]
- Node Versions or other

**Additional context**
Add any other context about the problem here.

Start the project and reproduce the logged-out state described in the issue. Locate the header component and the logic controlling its visibility, then verify that logged-out users no longer see the header or its logout button.

Written by the indexing model from the issue text.