Mejorado Documentation

Approved the Coaching specification

Internal: the nine open decisions in docs/specs/COACHING.md are settled, and the specification is approved.

Internal: docs/specs/COACHING.md is approved. The area is called Coaching; an engagement is open to its coaches and the team's admins; the app gets coach and client screens; Free has 3 open engagements and Pro and Team no limit; a coaching Video Chat call runs to its session length plus 15 minutes, up to 120; there are no SMS reminders; client writing pages show a fixed emergency line and the coach's own; Magpie writes no coaching agreement; and program pages with payment are in version 1. Nothing is built yet.