Add Bitbucket repository support

[akuligowski9]

Summary

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

Details

Similar to the GitLab support request (#2), adding Bitbucket would broaden the user base to developers who host code on Bitbucket.

Approach

• Create engine/projectbridge/input/bitbucket.py following the same pattern as github.py
• Extract languages, frameworks, infrastructure signals from Bitbucket's API
• Add --bitbucket-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
• Bitbucket REST API docs