Merge latest Library.Template

[AArnott]

• Clarify what looks like bad wording
• Update nbgv and nerdbank.gitversioning updates to 3.10.91 (538)
• Cache the dotnet-install scripts locally
• Update Microsoft Testing Platform to 2.3.1 (539)
• Reapply update to dotnet-coverage 18.9.0 (536)
• Move AI files to a more generic place
• Update Microsoft Testing Platform to 2.3.2 (VSTHRD103 should allow calling Task.Result after awaiting Task.WhenAll #541)
• Bump .NET SDK to v10.0.302 (VSTHRD010 does not recognize switches OFF the main thread #542)
• Update .NET packages to 4.0.732401
• Update dependency Microsoft.CodeAnalysis.Analyzers to 5.6.0

[Copilot]

Pull request overview

This PR merges the latest Library.Template changes into vs-threading, primarily updating SDK/tooling/dependency versions and switching the repo’s .NET SDK install flow to use locally cached dotnet-install scripts rather than downloading them on demand.

Changes:

• Cache dotnet-install.ps1 / dotnet-install.sh in tools/ and add an updater script to refresh them from dotnet/install-scripts.
• Bump the repo .NET SDK (global.json) and update key dependencies/tools (e.g., Microsoft Testing Platform, Nerdbank.GitVersioning, dotnet-coverage).
• Add agent/skill documentation files used for future template merges and dependency PR workflows.

Reviewed changes

Copilot reviewed 8 out of 12 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tools/Update-DotNetInstallScript.ps1	New script to refresh cached dotnet-install scripts from upstream.
tools/Install-DotNetSdk.ps1	Adjusted to use cached dotnet-install scripts from tools/.
tools/GitHubActions.ps1	Clarifies exception messages for missing GITHUB_ENV / GITHUB_PATH.
tools/dotnet-install.sh	Vendored dotnet-install bash script into repo for local caching.
tools/dotnet-install.ps1	Vendored dotnet-install PowerShell script into repo for local caching.
global.json	Bumps required .NET SDK version to 10.0.302.
Directory.Packages.props	Updates central versions (e.g., MTP 2.3.2, Roslyn analyzers alignment, diagnostics runtime).
.config/dotnet-tools.json	Updates tool versions (e.g., dotnet-coverage, nbgv).
AGENTS.md	Adds repo-specific Copilot/agent guidance documentation.
.agents/skills/update-library-template/template-release-notes.md	Adds template merge notes for future updates.
.agents/skills/update-library-template/SKILL.md	Adds skill instructions for merging from Library.Template.
.agents/skills/bundle-dependency-prs/SKILL.md	Adds skill instructions for bundling/fixing dependency PRs.

Comments suppressed due to low confidence (1)

tools/Install-DotNetSdk.ps1:301

• On macOS/Linux this script invokes tools/dotnet-install.sh via PowerShell's call operator (&). That requires the file to be executable, but the new caching flow (Update-DotNetInstallScript.ps1) can overwrite dotnet-install.sh without +x, causing "Permission denied" at runtime. Invoke the .sh script via bash to avoid relying on file permissions.

# In case the script we invoke is in a directory with spaces, wrap it with single quotes.
# In case the path includes single quotes, escape them.
$DotNetInstallScriptPathExpression = $DotNetInstallScriptPath.Replace("'", "''")
$DotNetInstallScriptPathExpression = "& '$DotNetInstallScriptPathExpression'"