The medication detail clients computed the supply headline in the browser
via summariseSupply, risking web/iOS drift and pulling the shared math
into the client bundle. The GET /api/medications/[id]/inventory route now
computes the canonical SupplySummary server-side through summariseSupply
(the single source of truth) and ships it in the DTO; the Bestand and
Übersicht surfaces render the ready figures. Adds the MedicationSupplySummary
schema to the inventory list response and regenerates the OpenAPI contract.