- Add seven_day_session_test.go with comprehensive test coverage:
- Test login returns 7-day session (expires_in: 604800)
- Test cookie MaxAge is 7 days (604800 seconds)
- Test refresh token returns 7-day access token
- Test JWT token has 7-day expiration claim
- Test 401 error handler redirects HTML requests
- Test 401 error handler returns JSON for API requests
- Test register/login do not set document.cookie
- Tests use getTestUserID() and setupTestServer() helpers
- Update security_test.go JWT expiration comment to reflect 7 days
Tests verify all aspects of the 7-day session implementation
including constants usage, cookie values, API responses, and
smart 401 error handling.