Changes backend in preparation for frontend work

src/SlpModularCms.Modules.Availability/Middleware/AvailabilityMiddleware.cs

@@ -1,6 +1,7 @@
 using System.IdentityModel.Tokens.Jwt;
 using System.Security.Claims;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Logging;
 using SlpModularCms.Core.Availability;
 using SlpModularCms.Core.Exceptions;
@@ -48,13 +49,17 @@ public class AvailabilityMiddleware
         _logger.LogWarning("Request geblokkeerd vanwege systeemstatus: {Status}. Path: {Path}", status, context.Request.Path);
 
         context.Response.StatusCode = StatusCodes.Status503ServiceUnavailable;
-        var response = new ApiErrorResponse(
-            Message: status == AvailabilityStatus.Maintenance 
+        var problemDetails = new ProblemDetails
+        {
+            Status = StatusCodes.Status503ServiceUnavailable,
+            Title = "Service Unavailable",
+            Detail = status == AvailabilityStatus.Maintenance 
                 ? "Het systeem is momenteel in onderhoud. Probeer het later opnieuw." 
-                : "De service is tijdelijk niet beschikbaar."
-        );
+                : "De service is tijdelijk niet beschikbaar.",
+            Instance = context.Request.Path
+        };
 
-        await context.Response.WriteAsJsonAsync(response);
+        await context.Response.WriteAsJsonAsync(problemDetails);
     }
 
     private bool IsAdminBypass(HttpContext context)