Voeg leesbare slug toe aan Offering naast het GUID-ID

Het Offering-ID is een GUID en niet geschikt om aan gebruikers te tonen.
Voeg een op de titel gebaseerde, unieke slug toe die via de public en
admin API wordt meegegeven, zodat de frontend iets leesbaars kan tonen
in plaats van het ruwe ID. Het ID blijft ongewijzigd de echte identifier.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/SlpModularCms.Modules.Offerings/Services/OfferingsService.cs

@@ -25,6 +25,7 @@ public class OfferingsService(IOfferingRepository repository, ILogger<OfferingsS
         var offering = new Offering
         {
             Id = Guid.NewGuid(),
+            Slug = await GenerateUniqueSlugAsync(request.Title),
             Title = request.Title,
             Description = request.Description,
             Price = request.Price,
@@ -69,6 +70,9 @@ public class OfferingsService(IOfferingRepository repository, ILogger<OfferingsS
         if (offering is null)
             return null;
 
+        if (!string.Equals(offering.Title, request.Title, StringComparison.Ordinal))
+            offering.Slug = await GenerateUniqueSlugAsync(request.Title, excludeId: offering.Id);
+
         offering.Title = request.Title;
         offering.Description = request.Description;
         offering.Price = request.Price;
@@ -202,8 +206,24 @@ public class OfferingsService(IOfferingRepository repository, ILogger<OfferingsS
         repository.Update(current);
     }
 
+    private async Task<string> GenerateUniqueSlugAsync(string title, Guid? excludeId = null)
+    {
+        var baseSlug = Slugifier.Slugify(title);
+        var slug = baseSlug;
+        var suffix = 2;
+
+        while (await repository.ExistsBySlugAsync(slug, excludeId))
+        {
+            slug = $"{baseSlug}-{suffix}";
+            suffix++;
+        }
+
+        return slug;
+    }
+
     private static OfferingDto ToPublicDto(Offering o) => new(
         o.Id.ToString(),
+        o.Slug,
         o.Title,
         o.Description,
         o.Price,
@@ -215,6 +235,7 @@ public class OfferingsService(IOfferingRepository repository, ILogger<OfferingsS
 
     private static OfferingAdminDto ToAdminDto(Offering o) => new(
         o.Id.ToString(),
+        o.Slug,
         o.Title,
         o.Description,
         o.Price,