Fix CI build failure: switch to msbuild + rebase onto update-bump

[Copilot]

The windows-latest runner now ships with .NET SDK 10.0.102, causing two CI failures that are fixed by this PR:

1. MSB4019: dotnet build sets MSBuildExtensionsPath to the dotnet SDK directory, which doesn't include Microsoft\DesktopBridge\. Fixed by switching to msbuild.

2. CsWinRT Platform.xml error: After fixing MSB4019, CsWinRT failed because Platform.xml for Windows SDK 10.0.22621.0 is not present on the runner (C:\Program Files (x86)\Windows Kits\10\Platforms\UAP\10.0.22621.0\Platform.xml). Fixed by rebasing onto update-bump, which upgrades the target SDK to 10.0.26100.0 (installed on the runner).

Changes

• .github/workflows/build.yml: Replace dotnet restore/dotnet build with msbuild (already on PATH via microsoft/setup-msbuild@v2), which resolves MSBuildExtensionsPath to the Visual Studio installation where DesktopBridge targets are present.

# Before
- name: Restore dependencies
  run: dotnet restore "Simple Icon File Maker.sln"
- name: Build solution
  run: dotnet build "Simple Icon File Maker.sln" --configuration Release --no-restore

# After
- name: Restore dependencies
  run: msbuild "Simple Icon File Maker.sln" /t:Restore /p:Configuration=Release /p:Platform=x64
- name: Build solution
  run: msbuild "Simple Icon File Maker.sln" /p:Configuration=Release /p:Platform=x64

• All update-bump branch changes applied, including:
  • TargetFramework / TargetPlatformVersion bumped from 10.0.22621.0 → 10.0.26100.0
  • NuGet package updates (WindowsAppSDK, SDK.BuildTools, CommunityToolkit, Magick.NET, etc.)
  • New AI background removal feature (BackgroundRemoverHelper.cs, RemoveBackgroundDialog)
  • Updated Package.appxmanifest with share target extension and systemAIModels capability
  • Removed FodyWeavers.xml / PropertyChanged.Fody

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[TheJoeFin]

@copilot rebase on to update-bump, then fix https://github.com/TheJoeFin/Simple-Icon-File-Maker/actions/runs/22652184257/job/65654061782?pr=66

[Copilot]

@copilot rebase on to update-bump, then fix https://github.com/TheJoeFin/Simple-Icon-File-Maker/actions/runs/22652184257/job/65654061782?pr=66

Done in 0dc41cf. The changes from update-bump have been applied to this branch, including the key fix: upgrading TargetPlatformVersion and TargetFramework from 10.0.22621.0 to 10.0.26100.0.

The new CI failure (CsWinRT Platform.xml error) was caused by CsWinRT looking for Platform.xml at C:\Program Files (x86)\Windows Kits\10\Platforms\UAP\10.0.22621.0\Platform.xml — a version not present on the runner. With the SDK version bumped to 10.0.26100.0 (which matches what's installed on windows-latest), that error should be resolved.