Coaching: clients, goals, actions, habits and check-ins (preview)

Internal: Coaching is a site-admin preview (docs/specs/COACHING.md, handoff in docs/plans/COACHING.md). A coach adds a client by name and email address, which makes a Draft with a weekly check-in, a Contact if needed, and a Client Portal for that one person that only the client's coaches and team admins can list, open or preview. Start coaching emails the portal invitation with the coach's welcome message. Goals are measured by a number, a rating, done or not, or five levels, with milestones, a chart and Behind for coaches; actions have owners, due dates, when-and-where plans and outcomes with what was learned; habits show consistency against their own target and a grid of weeks, never a streak; check-ins open on a schedule in the client's time zone, keep answers as they are typed, record goal values and log habits. The Overview lists answers waiting, clients who need attention with Seen, and coaching ending soon. The client works with all of it in a Coaching section of their portal. Free has 3 open coaching clients. Sessions, reminders, exercises, programs, payments, sponsors, cohorts, export and the app are not built.