Allow anyone to request to be Early Crew

Anyone can say "I want to volunteer" but we don't need 60+ volunteers. Socials and Potter should be the ONLY ones able to accept a volunteer, and instead of a deny button, there should be a DEFER button so that IF early crew needs help (like if a bunch of Early Crew gets hit by a bazooka) socials has people to ask

Start by locating the volunteer request and Early Crew acceptance flow in the Python web app, then read any existing tests for volunteer roles or status changes. Confirm how Socials and Potter permissions are represented and how a deferred request should remain available for later outreach; done means unauthorized users cannot accept requests and defer replaces deny.

索引モデルが issue の本文から書いたものです。