Create or update a company

Create or update a company by its external companyId (upsert). Only name, plan, domain, value, sla, tags, address and customData are accepted; any other field is ignored. tags REPLACES the stored list (an empty array clears it), while address and customData are merged into the existing values rather than replaced. customData accepts up to 100 primitive values, tags up to 50. Setting a non-empty name here marks it authoritative, so names sent by the SDK will no longer overwrite it.