People remain in intromembers group after Spring Evals

When someone passes their first spring evals, they're supposed to be removed from the intro members group. That currently doesn't happen and has to be done manually. This should be part of the Evals flow.

未指定檔案或測試。請在儲存庫中搜尋 Evals 流程和 intromembers 群組的處理邏輯，然後追蹤成員通過其第一次 spring evals 後會發生什麼。完成的標準是，成功完成後會自動將成員從群組中移除，無需手動清理。

由索引模型根據 Issue 內容生成。