Add isolated question completion credits

api/QuestionsApi/Controllers/CreditsController.cs

@@ -0,0 +1,20 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using QuestionsApi.Services;
+using System.Security.Claims;
+
+namespace QuestionsApi.Controllers;
+
+[ApiController]
+[Route("api/credits")]
+[Authorize(Roles = "USER,SUPER")]
+public sealed class CreditsController(CreditStore credits) : ControllerBase
+{
+    [HttpGet]
+    public async Task<IActionResult> Get() => Ok(await credits.GetStatusAsync(UserId()));
+
+    private string UserId() => User.FindFirstValue(ClaimTypes.NameIdentifier)
+        ?? User.FindFirstValue(ClaimTypes.Name)
+        ?? User.Identity?.Name
+        ?? throw new UnauthorizedAccessException();
+}