Fix type alias target graph edges

[Widthdom]

Summary

• Add explicit type_alias_target references for Swift and TypeScript type alias RHS expressions.
• Include type_alias_target in graph traversal reference kinds and the valid reference-kind catalog.
• Add regression coverage for Swift and TypeScript alias target edges.

Validation

• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false
• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj -c Release --framework net8.0 --filter "FullyQualifiedName~ReferenceExtractorTests.Extract_TypeScriptTypeAliasGenericDefaults_EmitsDefaultAndRhsTypeReferences|FullyQualifiedName~ReferenceExtractorTests.Extract_SwiftTypealiasRhs_RecordsReferencedTypes|FullyQualifiedName~QueryCommandRunnerTests.RunSymbols_SwiftKindFiltersSeparateTypealiasAssociatedtypeAndProtocol" -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check

Documentation and Changelog

• Added changelog fragment changelog.d/unreleased/1976.fixed.md.

Review

• Adversarial review: No blocking/actionable issues found.

Fixes #1976

[Widthdom]

Closing without merge because #1976 was already completed by #2785 (merged into main as 9d90261). That PR added the changelog fragment changelog.d/unreleased/1976.fixed.md and the corresponding implementation/tests, so this PR now conflicts with main and is superseded.