Look up V3 IDs for one or more V1 (legacy) IDs for companies that were migrated
from the V1 platform. Pass the V1 ID as the query-parameter value.

For scalar entities (locationId, serviceId, etc.), each requested key maps to a
single V3 UUID string or null when no mapping exists for the authenticated company.

For allocationId, the value is always a JSON array of V3 UUID strings (possibly
empty): one V1 allocation can expand into multiple single allocations after migration,
so multiple rows may share the same legacyId.

Mappings are scoped to the authenticated company. At least one of the supported
entity query parameters must be provided.

Supported parameters: locationId, serviceId, resourceId, customerId,
appointmentId, companyId, allocationId.