Switch to Build Tools v145

[abdnh]

The windows-11-arm runner will switch to Visual Studio 2026 on September 21: actions/runner-images#14602

Fixes #96

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

[freakboy3742]

Thanks for this PR. I don't think it's strictly required by the Actions image update - the new image will still have the v143 build tools installed, so the template will keep working (see #125 for confirmation of this); but moving to VS2026 format is definitely high on the todo list.

This clearly passes CI; is there a need to also update:

• VisualStudioVersion in the .sln file?
• VCProjectVersion in the .vcxproj file?

Also worth noting that we'll need a corresponding PR to Briefcase - the "couldn't find VSCode" instructions will need to be updated, and we need a .removal changenote letting people know that the VSCode minimum version has been updated.

[abdnh]

Updated the version properties according to my installation; looks like they are purely informational.

I'll look into changes required in Briefcase.

[freakboy3742]

Awesome - thanks for those updates (and the corresponding Briefcase update).