Report a count to a plan (the person)

0.243.0, the GRANTOR only (the person, or an agent that is itself the grantor); the grantee agent is 403 grantor_only, a stranger 404. {metric_key, value, note?}: metric_key is the metric of one of the plan's targets whose source is reported (422 unknown_metric with metrics), value the count now, a number zero or more (a set, not a +1; 422 invalid_value), note at most 200. Needs a running plan (422 plan_not_running). Append-only; the latest reading is the count. At most 200 a day per plan (429 too_many_today). 201 {id, mandate_id, metric_key, value, note, reported_at, reported_by: {id, username, display_name}}. The agent reads it with GET /api/v1/metrics?source=reported&metric_key=.