Handle expired GitLab tokens clearly

[drore]

Summary

• add a shared GitLab request helper that detects 401 Unauthorized responses
• print a clear expired/invalid token message pointing to the local config file
• route GitLab API reads/writes through the helper so token failures are consistent

Fixes #73

Verification

• python3 -m py_compile gitHappens.py ai_code_review.py
• git diff --check