feature: HL7 FHIR R4 Integration

VigilCareRecordsAPI/Controllers/Fhir/FhirEncounterController.cs

@@ -0,0 +1,42 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+[ApiController]
+[Route("fhir/Encounter")]
+[Produces("application/fhir+json")]
+[Authorize]
+public class FhirEncounterController : ControllerBase
+{
+    private readonly IFhirService _fhir;
+
+    public FhirEncounterController(IFhirService fhir) => _fhir = fhir;
+
+    /// <summary>
+    /// FHIR read: GET /fhir/Encounter/{id}
+    /// </summary>
+    [HttpGet("{id}")]
+    public async Task<IActionResult> Read(string id)
+    {
+        var encounter = await _fhir.GetEncounterAsync(Guid.Parse(id));
+        if (encounter is null)
+            return NotFound(FhirErrorHelper.NotFound("Encounter", id));
+
+        return Ok(encounter);
+    }
+
+    /// <summary>
+    /// FHIR search: GET /fhir/Encounter?patient=X&status=Y&date=Z
+    /// Supports search by patient reference, status, and date range.
+    /// </summary>
+    [HttpGet]
+    public async Task<IActionResult> Search(
+        [FromQuery] string? patient,
+        [FromQuery] string? status,
+        [FromQuery] string? date,
+        [FromQuery(Name = "_count")] int count = 20,
+        [FromQuery(Name = "_offset")] int offset = 0)
+    {
+        var bundle = await _fhir.SearchEncountersAsync(patient, status, date, count, offset);
+        return Ok(bundle);
+    }
+}