Converts natural language text into a structured FHIR resource.

Patient identifier handling. When generating a patient (or patient-canvas) resource, US Core requires Patient.identifier (a business identifier such as an MRN). When the source text contains an identifier, it is extracted with an appropriate URI system. When the source text does not contain a detectable identifier, a synthetic one is generated with system: "urn:phenoml:lang2fhir-generated-id" and a UUID value so the resource remains FHIR-valid and US Core conformant. Callers who need a tenant-specific namespace should rewrite the synthetic system after extraction.