gws issue picker: add GitLab/Bitbucket support

[tasuku43]

Summary

Extend the interactive issue picker (gwst create --issue without URL) to support GitLab and Bitbucket issue lists.

Notes

• Current picker uses gh api (GitHub only).
• For GitLab / Bitbucket, use the respective APIs (or CLIs, if we decide) to fetch open issues.
• Preserve existing URL mode behavior.

Acceptance

• When the repo host is GitLab or Bitbucket, gwst create --issue can list and select open issues.
• Errors are clear when authentication or requests fail.
• Tests cover parsing and mapping of issue lists per provider.