Refactor build/versioning: shell-agnostic builds, auto NuGet versioning, and Copilot-ready workflow

[yeelam-gordon]

Description

1. Build from any Command Prompt or PowerShell (no VS 2022 Developer Command Prompt required), helping folks who prefer VS Code
2. UpdateVersion auto-resolves the correct NuGet package version (no more pre-downloading package folders)
3. Copilot works seamlessly in both Visual Studio and VS Code with the new copilot-instructions.md

Build system modernization:

• Introduced a new build.ps1 PowerShell script that replaces the logic previously in build.cmd, providing robust solution discovery, environment initialization, NuGet package management, and MSBuild invocation with improved diagnostics and usage documentation. (build.ps1)
• Refactored build.cmd to become a thin wrapper that simply invokes build.ps1, removing all direct build, restore, and timing logic from the batch script. (build.cmd)

Versioning improvements:

• Updated UpdateVersions.ps1 to require the WinAppSDKVersion parameter and add logic to ensure the necessary NuGet packages are downloaded and available before proceeding, improving reliability for version bumps. (UpdateVersions.ps1)

Contributor guidance:

• Added a new .github/copilot-instructions.md file documenting build usage, versioning steps, coding guidelines, PR process, and design doc practices to ensure consistent and high-quality contributions. (.github/copilot-instructions.md)

Target Release

Please specify which release this PR should align >=1.8

Checklist

Note that /azp run currently isn't working for this repo.

• Samples build and run using the Visual Studio versions listed in the Windows development docs.
• Samples build and run on all supported platforms (x64, x86, ARM64) and configurations (Debug, Release).
• Samples set the minimum supported OS version to Windows 10 version 1809.
• Samples build clean with no warnings or errors.
• [For new samples]: Samples have completed the sample guidelines checklist and follow standardization/naming guidelines.
• Microsoft employees only: you can validate your changes by following the instructions here: https://www.osgwiki.com/wiki/WindowsAppSDK-Samples

[Copilot]

Pull Request Overview

This PR modernizes the build system for WindowsAppSDK-Samples by introducing a new PowerShell-based build script, improving version management, and adding contributor guidance.

• Refactored build system from batch to PowerShell with automatic environment detection and improved diagnostics
• Enhanced UpdateVersions.ps1 to require WinAppSDKVersion parameter and auto-download necessary NuGet packages
• Added comprehensive contributor guidance in .github/copilot-instructions.md

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
build.ps1	New PowerShell build script with robust solution discovery, VS environment initialization, and MSBuild invocation
build.cmd	Refactored to thin wrapper that calls build.ps1, removing complex batch logic
UpdateVersions.ps1	Made WinAppSDKVersion parameter mandatory and added automatic NuGet package installation
.github/copilot-instructions.md	New contributor guidance covering build usage, versioning, coding guidelines, and PR processes

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[Copilot]

The comment '#[CmdletBinding()] parameters' is grammatically incorrect. It should be '#[CmdletBinding()] param' or a more descriptive comment like '# Parameters definition'.

Suggested change

	#[CmdletBinding()] parameters
	# Parameters definition

[Copilot]

Inconsistent indentation: this function and the following Build-Solution function have an extra leading space compared to other functions. All functions should use consistent indentation.

Suggested change

	# Restore-Solution: Perform NuGet restore for a solution (.sln) using repo nuget.exe.
	function Restore-Solution { param([string]$SolutionPath)
	Write-Host "Restoring: $SolutionPath" -ForegroundColor Cyan
	& $nugetExe restore $SolutionPath -ConfigFile (Join-Path $samplesRoot 'nuget.config') -PackagesDirectory $packagesDir
	if ($LASTEXITCODE -ne 0) { Write-Error 'NuGet restore failed.'; exit $LASTEXITCODE }
	}
	# Build-Solution: Invoke MSBuild on a solution with platform/config and emit binlog.
	function Build-Solution { param([string]$SolutionPath,[string]$Platform,[string]$Configuration)
	$binlog = Join-Path (Split-Path $SolutionPath -Parent) ("{0}.binlog" -f ([IO.Path]::GetFileNameWithoutExtension($SolutionPath)))
	Write-Host "Building: $SolutionPath" -ForegroundColor Cyan
	& msbuild /warnaserror /p:Platform=$Platform /p:Configuration=$Configuration /p:NugetPackageDirectory=$packagesDir /bl:"$binlog" "$SolutionPath"
	if ($LASTEXITCODE -ne 0) { Write-Error 'MSBuild failed.'; exit $LASTEXITCODE }
	}
	# Restore-Solution: Perform NuGet restore for a solution (.sln) using repo nuget.exe.
	function Restore-Solution { param([string]$SolutionPath)
	Write-Host "Restoring: $SolutionPath" -ForegroundColor Cyan
	& $nugetExe restore $SolutionPath -ConfigFile (Join-Path $samplesRoot 'nuget.config') -PackagesDirectory $packagesDir
	if ($LASTEXITCODE -ne 0) { Write-Error 'NuGet restore failed.'; exit $LASTEXITCODE }
	}
	# Build-Solution: Invoke MSBuild on a solution with platform/config and emit binlog.
	function Build-Solution { param([string]$SolutionPath,[string]$Platform,[string]$Configuration)
	$binlog = Join-Path (Split-Path $SolutionPath -Parent) ("{0}.binlog" -f ([IO.Path]::GetFileNameWithoutExtension($SolutionPath)))
	Write-Host "Building: $SolutionPath" -ForegroundColor Cyan
	& msbuild /warnaserror /p:Platform=$Platform /p:Configuration=$Configuration /p:NugetPackageDirectory=$packagesDir /bl:"$binlog" "$SolutionPath"
	if ($LASTEXITCODE -ne 0) { Write-Error 'MSBuild failed.'; exit $LASTEXITCODE }
	}

[Copilot]

Inconsistent indentation: this function has an extra leading space compared to other functions. All functions should use consistent indentation.

Suggested change

	# Build-Solution: Invoke MSBuild on a solution with platform/config and emit binlog.
	function Build-Solution { param([string]$SolutionPath,[string]$Platform,[string]$Configuration)
	# Build-Solution: Invoke MSBuild on a solution with platform/config and emit binlog.
	function Build-Solution { param([string]$SolutionPath,[string]$Platform,[string]$Configuration)

[Copilot]

The comment has a trailing comma that should be removed for proper grammar.

Suggested change

	# If the NuGetPackagesFolder parameter wasn't provided,
	# If the NuGetPackagesFolder parameter wasn't provided