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.Tests/Services/OfferingsServiceTests.cs

@@ -27,6 +27,7 @@ public class OfferingsServiceTests
     private static Offering ExistingOffering(bool featured = false, int displayOrder = 0) => new()
     {
         Id = Guid.NewGuid(),
+        Slug = "existing",
         Title = "Existing",
         Description = "Description",
         Price = "€ 100",
@@ -91,6 +92,57 @@ public class OfferingsServiceTests
         await _repo.DidNotReceive().BeginTransactionAsync();
     }
 
+    // --- Slug generation ---
+
+    [Fact]
+    public async Task CreateAsync_GeneratesSlugFromTitle()
+    {
+        _repo.GetMaxDisplayOrderAsync().Returns(-1);
+
+        var dto = await CreateSut().CreateAsync(CreateRequest(), Guid.NewGuid());
+
+        dto.Slug.Should().Be("title");
+    }
+
+    [Fact]
+    public async Task CreateAsync_AppendsSuffix_WhenSlugAlreadyTaken()
+    {
+        _repo.GetMaxDisplayOrderAsync().Returns(-1);
+        _repo.ExistsBySlugAsync("title", null).Returns(true);
+        _repo.ExistsBySlugAsync("title-2", null).Returns(true);
+        _repo.ExistsBySlugAsync("title-3", null).Returns(false);
+
+        var dto = await CreateSut().CreateAsync(CreateRequest(), Guid.NewGuid());
+
+        dto.Slug.Should().Be("title-3");
+    }
+
+    [Fact]
+    public async Task UpdateAsync_RegeneratesSlug_WhenTitleChanges()
+    {
+        var target = ExistingOffering();
+        _repo.GetByIdAsync(target.Id).Returns(target);
+        _repo.ExistsBySlugAsync("new-title", target.Id).Returns(false);
+
+        var request = new UpdateOfferingRequest("New Title", "Description", "€ 100", "per month", ["Feature 1"], "Contact");
+        var dto = await CreateSut().UpdateAsync(target.Id, request, Guid.NewGuid());
+
+        dto!.Slug.Should().Be("new-title");
+    }
+
+    [Fact]
+    public async Task UpdateAsync_KeepsExistingSlug_WhenTitleUnchanged()
+    {
+        var target = ExistingOffering();
+        _repo.GetByIdAsync(target.Id).Returns(target);
+
+        var request = new UpdateOfferingRequest(target.Title, "Description", "€ 100", "per month", ["Feature 1"], "Contact");
+        var dto = await CreateSut().UpdateAsync(target.Id, request, Guid.NewGuid());
+
+        dto!.Slug.Should().Be("existing");
+        await _repo.DidNotReceive().ExistsBySlugAsync(Arg.Any<string>(), Arg.Any<Guid?>());
+    }
+
     // --- UpdateAsync ---
 
     [Fact]