feat(drive): add commenter role to drive share

[pavelzak]

Summary

• Add commenter as a valid permission role for drive share --role
• Allows sharing files with comment-only access, matching the Google Drive API's commenter role
• Updates help text, validation, and constants accordingly

Test plan

• Run drive share --role=commenter --to=user --email=test@example.com <fileId> and verify commenter permission is applied
• Verify drive share --role=invalid still returns an error
• Verify default role remains reader

[steipete]

Landed manually on main with added coverage for commenter role output.

• Commit: c92d2e6 feat(drive): support commenter share role (feat(drive): add commenter role to drive share #443)
• Gate: make ci
• Live: uploaded a temporary Drive file with clawdbot@gmail.com, shared it to steipete@gmail.com as commenter, verified the returned role, then trashed the test file.

Thanks @pavelzak!