FHIR API endpoint to serve R4 resources

[Mosss-OS]

Description

FHIR R4 mapping types exist in src/lib/fhir.ts (1057 lines) but there is no API endpoint. This would enable interoperability with health information systems.

Current State

• FHIR mapping functions exist (Patient, Observation, Condition, ClinicalImpression)
• No API endpoint to serve FHIR resources

Required Changes

1. Create server API routes (/api/fhir/Patient, /api/fhir/Observation, etc.)
2. Implement FHIR search/read operations from IndexedDB
3. Return proper FHIR JSON bundles
4. Support basic query parameters (_id, _lastUpdated, _count)
5. Add auth/authorization