Fix: show the API path hint when a bare address redirects

[SandObserver]

Summary

• Show the missing-API-path hint for a bare address that answers with a redirect (upstream.redirect), the usual result of a service root sending the request to its login page.
• Stop treating a plain invalid code as a missing path: the badge proxy returns it only for malformed requests, and a page that is not data already reaches the no-values hint on the success path.

Testing
All green. Moved the redirect case into the hint test and invalid into the known-cause test.

Changelog

Checklist

• Stays within the project constraints: one container, no runtime dependencies, no build step (see CONTRIBUTING.md).
• Tests added or updated for new logic, and the full suite, lint, and typechecks pass.
• Docs updated if behavior or configuration changed.