Improve UX: Forbidden requests should not redirect to login page

Describe the bug
When the user opens a page they don't have access to, the app will redirect them to the login page. This is not optimal since the user does NOT need to re-auth. They don't have the required permission, and signing in again will only result in facing the same login page. Hence a broken loop.
As a side note, it's a bit disruptive too, since the sidebar does not exist on the login page, making it non-trivial to go back to the page they were before.

To Reproduce
Steps to reproduce the behavior:

1. Sign in as a user that doesn't have the required permission to open e.g. a specific namespace
2. Switch to that specific namespace
3. You will get redirected to the login page

Expected behavior
The user should be made aware that they do not have the required permission, and they should probably ask their administrator to grant them the required permissions if they need to access this page.

Desktop (please complete the following information):

• OS: Any
• Browser: Any
• Version: 2.28.11

Start by tracing how forbidden namespace requests are handled and where they are redirected to the login page. Reproduce the scenario with a signed-in user lacking permission, then verify that the app shows a clear permission message and keeps the user out of the login redirect loop.