Imaging: Upgrade ImageSharp to v4 (keep v2 as a supported option)

[AndyButland]

Description

Upgrades the default imaging package (Umbraco.Cms.Imaging.ImageSharp) from ImageSharp 3 to ImageSharp 4, keeping Umbraco.Cms.Imaging.ImageSharp2 (ImageSharp 2) as a supported option. The dedicated ImageSharp 3 package is not retained.

Licensing context. ImageSharp 4 adds a build-time licence check for projects that reference it directly (the Split License terms are unchanged from v3 — only enforcement is new). Because this is a public, open-source repository we cannot commit a licence key, so both package references use ExcludeAssets="build". The licence check ships in the package's MSBuild build/ assets, so excluding them means the CMS builds with no sixlabors.lic for CI, contributors and forks, while the compile/runtime assets flow normally and the library is unaffected.

• Umbraco sites consume ImageSharp transitively and need no licence.
• Only a project adding its own direct PackageReference to SixLabors.ImageSharp[.Web] is subject to the check.
• Umbraco holds a free Six Labors Community/OSS licence for compliance, kept out of the source tree.

Changes

• Directory.Packages.props: SixLabors.ImageSharp and SixLabors.ImageSharp.Web → 4.0.0.
• Umbraco.Cms.Imaging.ImageSharp.csproj: ExcludeAssets="build" on both references.
• UmbracoBuilderExtensions.cs: one namespace fix — v4 moved the DI/pipeline extensions (AddImageSharp, AddProvider, AddProcessor, ClearProviders, UseImageSharp) from SixLabors.ImageSharp.Web.DependencyInjection to the root SixLabors.ImageSharp.Web namespace.
• Updated the two imaging CLAUDE.md files (v4 references, licensing/build notes).

The Umbraco.Cms.Imaging.ImageSharp2 project and the Umbraco.Cms meta-package reference are unchanged.

Testing

Solution should build and CI checks pass; existing ImageSharp unit tests (ImageSharpImageUrlGeneratorTests, CropWebProcessorTests) cover URL generation and crop maths.

Cropped images should continue to be served at the expected dimensions on a running site.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud