User Story: Improve Error Messages

[givecoffee]

As a user, I want there to be clear error messages when authentication or other connections fail so that I know how to resolve the problem.

Criteria to meet this:

• Replace the generic "Auth error" popup with specific messages on whether the token is expired, the login credentials are invalid, or missing tokens
• Display user-friendly messages on the front end and detailed logs on the backend
• Add a link to "Re-Authenticate" or "Login" when the token is stale
• Test with expired/invalid tokens