Rename workspace role display names from Contributor to Creator

[yousoph]

Summary

• Renames display names for three workspace roles: Primary/Secondary/Limited Contributor → Primary/Secondary/Limited Creator
• Underlying role identifiers (PresetAlpha, PresetBeta, PresetGamma) remain unchanged
• Updates both source code and tests

Test plan

• All 64 existing tests in main_test.py and export_users_test.py pass
• Verify role display names appear correctly in the UI after import/export operations

🤖 Generated with Claude Code

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[sadpandajoe]

I believe this PR is a breaking change moving forward. They way it shoudl work is support both for now, and then we deprecate the old names later.

[Vitor-Avila]

Requesting some changes to make it backwards compatible

[Vitor-Avila]

I believe we can keep these changes as-is (new exports will include the updated name). We just need to make sure to only merge this once the change is live.

[Vitor-Avila]

But here we should keep these + add the new names. This way the import would support both old and new exports.

[Vitor-Avila]

@yousoph you'll also need to sign the CLA here