Add GitLab repository support

[akuligowski9]

Summary

Extend the repository analyzer to support GitLab as an input source alongside GitHub.

Details

Currently ProjectBridge only analyzes GitHub repositories via the REST API (engine/projectbridge/input/github.py). Adding GitLab support would allow developers who host code on GitLab to use ProjectBridge.

Approach

• Create engine/projectbridge/input/gitlab.py following the same pattern as github.py
• Extract languages, frameworks, infrastructure signals from GitLab's API
• Add --gitlab-user CLI flag (mutually exclusive with --github-user)
• Normalize output to the same dev_context format the analysis engine expects

References

• GitHub analyzer: engine/projectbridge/input/github.py
• GitLab REST API docs