test(auth): add authentication coverage

[alucero270]

test(auth): add authentication coverage

Summary

Add automated coverage for authentication behavior so user identity flows are safe to evolve.

Scope

• Files: authentication tests, fixtures, verification docs as needed
• Components: authentication, login or token handling, user identity validation

Acceptance Criteria

• tests cover successful authenticated access behavior
• tests cover failed or invalid authentication flows
• tests pass in a documented verification flow

Notes

• Milestone 6 is not complete unless authentication tests are passing