feat(hts): synthesise parent/child/inactive properties + definition i…

[smunini]

…n $lookup

The HL7 tx-ecosystem simple-cases/simple-lookup-1 and simple-lookup-2 fixtures send property=* and expect $lookup to surface several "well-known" concept properties that aren't stored directly in concept_properties:

• parent — derived from concept_hierarchy.parent_code WHERE child_code = req.code
• child — derived from concept_hierarchy.child_code WHERE parent_code = req.code
• inactive — boolean derived from a status property in the FHIR inactive set (retired/deprecated/withdrawn/inactive); skipped when the concept already has an explicit inactive row to avoid duplicates
• definition — top-level Parameters entry sourced from concepts.definition

Each synthesised parent/child entry carries the related concept's display in description, matching the IG fixtures' optional description parts.

The wildcard handling and explicit-property filter both honour synthesised entries: property=* includes them all alongside stored properties; property=parent returns only the synthesised parent.

Both SQLite and PostgreSQL backends are updated. LookupResponse gains a definition: Option<String> field, surfaced by process_lookup as a top-level definition parameter.

Adds 8 unit tests (parent/child/inactive synthesis, no-status fallback, explicit-inactive non-duplication, definition echo, filtered selection, wildcard inclusion) and 1 HTTP-level integration test asserting the IG response shape end-to-end. All 499 helios-hts lib tests pass.