Prepare 0.3.0-alpha.3 release

[Aaronontheweb]

Summary

• bump the package suffix from alpha.2 to alpha.3
• add release notes for the PowerShell value/state analysis delivered in Promote PowerShell value and state analysis #133
• record the publication step as pending until the tag workflow succeeds

Validation

• adversarial release review: PASS
• dotnet build -c Release: clean, 0 warnings
• dotnet test -c Release --no-build: 2,765/2,765
• public API snapshots: 40/40
• dotnet pack: emitted ShellSyntaxTree.0.3.0-alpha.3.nupkg and .snupkg
• nuspec and both target-framework assemblies report 0.3.0-alpha.3
• public API diff against published alpha.2: empty for net8.0 and netstandard2.0
• release-note extraction for 0.3.0-alpha.3: verified
• strict OpenSpec validation, headers, and git diff checks: clean
• Slopwatch: no new findings