feat(11-04): add UpdateProfileAsync to ProfileService and ImportLogoFromBytesAsync to BrandingService

- ProfileService.UpdateProfileAsync: replaces profile by name and persists the change
- IBrandingService: add ImportLogoFromBytesAsync to interface contract
- BrandingService.ImportLogoFromBytesAsync: validates magic bytes, compresses if > 512KB, returns LogoData
- BrandingService.ImportLogoAsync: refactored to delegate to ImportLogoFromBytesAsync
- ProfileServiceTests: 2 new tests (UpdateProfileAsync happy path + KeyNotFoundException)
- BrandingServiceTests: 2 new tests (ImportLogoFromBytesAsync valid PNG + invalid bytes)
- Tests.csproj: suppress NU1701 for pre-existing LiveCharts2/OpenTK transitive warnings

SharepointToolbox.Tests/Services/ProfileServiceTests.cs

@@ -147,6 +147,32 @@ public class ProfileServiceTests : IDisposable
         await Assert.ThrowsAsync<KeyNotFoundException>(() => service.DeleteProfileAsync("NonExistent"));
     }
 
+    [Fact]
+    public async Task UpdateProfileAsync_UpdatesExistingProfile_AndPersists()
+    {
+        var service = CreateService();
+        var profile = new TenantProfile { Name = "UpdateMe", TenantUrl = "https://update.sharepoint.com", ClientId = "cid-update" };
+        await service.AddProfileAsync(profile);
+
+        // Mutate — set a ClientLogo to simulate logo update
+        profile.ClientLogo = new SharepointToolbox.Core.Models.LogoData { Base64 = "abc==", MimeType = "image/png" };
+        await service.UpdateProfileAsync(profile);
+
+        var profiles = await service.GetProfilesAsync();
+        Assert.Single(profiles);
+        Assert.NotNull(profiles[0].ClientLogo);
+        Assert.Equal("abc==", profiles[0].ClientLogo!.Base64);
+    }
+
+    [Fact]
+    public async Task UpdateProfileAsync_ProfileNotFound_ThrowsKeyNotFoundException()
+    {
+        var service = CreateService();
+        var profile = new TenantProfile { Name = "NonExistent", TenantUrl = "https://x.sharepoint.com", ClientId = "cid" };
+
+        await Assert.ThrowsAsync<KeyNotFoundException>(() => service.UpdateProfileAsync(profile));
+    }
+
     [Fact]
     public async Task SaveAsync_JsonOutput_UsesProfilesRootKey()
     {