feat(backend): scaffold ASP.NET Core Web API with health endpoint

backend/Controllers/HealthController.cs

@@ -0,0 +1,16 @@
+using Microsoft.AspNetCore.Mvc;
+
+namespace TarninaHub.Controllers;
+
+[ApiController]
+[Route("api/health")]
+public class HealthController : ControllerBase
+{
+    [HttpGet]
+    public ActionResult<HealthResponse> Get()
+    {
+        return Ok(new HealthResponse("ok"));
+    }
+}
+
+public record HealthResponse(string Status);