chore: Bump target framework to net10 and update years.

Upgrade project to .NET 10 and refresh copyright years.

- Change TargetFramework in src/Avalonia/Directory.Build.props from net9.0 to net10.0 to target .NET 10.
- Update copyright year range in LICENSE and src/Directory.Build.Props to 2018-2026.
- Add .DS_Store to .gitignore.

src/Directory.Build.Props

@@ -5,7 +5,7 @@
         <FileVersion>3.6.0.0</FileVersion>
         <AssemblyVersion>3.6.0.0</AssemblyVersion>
         <LangVersion>latest</LangVersion>
-        <Copyright>Copyright © HandyOrg 2018-2025</Copyright>
+        <Copyright>Copyright © HandyOrg 2018-2026</Copyright>
         <Authors>HandyOrg</Authors>
         <RepositoryUrl>https://github.com/HandyOrg/HandyControl</RepositoryUrl>
         <PackageProjectUrl>https://handyorg.github.io/</PackageProjectUrl>