Fix #11: bundled R4 schema is actually R5 — regenerate from R4 4.0.1, add R5 schema

[piotrszul]

Fixes #11.

Problem

schemas/fhir-schema-r4.json — used by default for every compilation and documented as FHIR R4 — was actually built from FHIR R5 5.0.0 definitions. I confirmed this: the committed file is byte-identical (same md5) to a schema freshly built from R5 source.

For R4 data, any element renamed/removed in R5 (e.g. Encounter.period, absent in R5 which renamed it to actualPeriod) failed to resolve, silently fell back to a JSON column type, and produced wrong/over-broad typing.

Fix (data regeneration — no code change)

The builder (scripts/build-fhir-schema.js) already produces correct output; only the committed artifact came from the wrong source version.

• Regenerated schemas/fhir-schema-r4.json from genuine R4 4.0.1 profiles-resources.json + profiles-types.json (8,503 keys).
• Added schemas/fhir-schema-r5.json built from R5 5.0.0 (this is the previous fhir-schema-r4.json content), for running ViewDefinitions against R5 via --schema-file.
• README: documented the bundled R5 schema.

Diff (current R5 → regenerated R4)

R5-only keys removed	3,960 (e.g. EncounterHistory, Encounter.actualPeriod)
R4 keys restored	1,780 (e.g. Encounter.period, statusHistory, classHistory)
Element types corrected	340 (e.g. ActivityDefinition.location: CodeableReference → Reference)

Verification: Encounter.period now types as STRUCT(start VARCHAR, end VARCHAR); the "unknown type" warnings disappear.

Tests

All 191 tests pass (bun test) against the regenerated R4 schema.

Note: the unrelated reserved-word quoting bug (e.g. Period.end) mentioned in #11 is a separate defect, out of scope here.