Mejorado Documentation

Added the plan for everyone having an account

Internal: docs/plans/EVERYONE_HAS_AN_ACCOUNT.md lists who uses Magpie without an account today and the work to give each of them one.

Internal: added docs/plans/EVERYONE_HAS_AN_ACCOUNT.md, a plan for the owner's rule of 18 October 2026 that everyone who uses Magpie has an account. It lists who already has one, the people who come back to something a member made for them by a link, a code or the Client Portal's own login, the one-off public actions still to be decided (booking, answering a form, buying, signing, registering), a recommended answer, the shared way to make or connect an account and hold an unconfirmed address, and the order of work. Apart from Coaching's sponsor contacts, nothing is built from it yet.