Change Group Membership as the Result of an Evaluation

Basically, we should check if someone is in the Intro Members group and if they fail Spring Evals they should be removed from both that group and the Active group when they fail.

Stretch goal: We should also remove people from Intro Members if they pass a Spring Eval.

Search the Python/Flask application for Spring Eval result handling and updates to the Intro Members and Active groups. Trace the existing membership-change path first, then verify that a failed evaluation removes the person from both groups; the stretch goal covers removal from Intro Members after a pass. Locate or add focused tests for these outcomes if the project has an established testing path.

Written by the indexing model from the issue text.