Practice metrics envelope (four practice widgets)

Returns the Home practice-metrics envelope: the two-axis widget catalog (services axis from the stored business model, ownership axis from the entity type), the practice config, the company's pinned widgets, and the four widgets assembled from the accountant-uploaded patient-free aggregate feed. Honest denominators: a widget whose inputs are absent reports available: false with the missing metric keys, and a figure whose denominator is unknown is null; nothing is fabricated (costPerCustomerCents: null means "cost per customer unknown"). Returns 404 unless practice_metrics is in the company's additionalMetrics list; the surface does not exist for an unlisted company.