Pilot Potential 6-Week long Packet

Close this issue if discussion moves against trying this, but there is discussion of changing packet to last for all six weeks and close for frosh as they hit 60%, so i'd love to see a branch that implements this so we can test it out for a semester and revert if we hate it.

See https://cshrit.slack.com/archives/CV0REE4JE/p1773708892372929 for discussion thread.

No files, tests, or entry points are named. Start by reviewing the existing packet lifecycle and the linked Slack discussion, then determine how a six-week packet and the 60% frosh-closing rule fit the current behavior. Done means a testable branch implements the proposed pilot without obscuring how to revert it.

Written by the indexing model from the issue text.