Fix Python metaclass hook references

[Widthdom]

Summary

• Emit Python base-class references from mixed class Derived(Base, Mixin, metaclass=Meta) headers without treating keyword arguments as base types.
• Suppress phantom Python super call rows while preserving the __init_subclass__ hook call edge from super().__init_subclass__().
• Add regression coverage for mixed metaclass headers and super().__init_subclass__() calls.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter "FullyQualifiedName~ReferenceExtractorTests" -p:UseSharedCompilation=false
• dotnet run --project tools/CodeIndex.Changelog -- check
• dotnet build CodeIndex.sln -c Release -p:UseSharedCompilation=false
• dotnet test CodeIndex.sln -c Release -p:UseSharedCompilation=false
• Adversarial review: No blocking/actionable issues found.

Documentation and Changelog

• Added bilingual changelog fragment: changelog.d/unreleased/2058.fixed.md
• No README or guide updates required; this is extractor behavior covered by tests and changelog.

Follow-up Candidates

• None.

Fixes #2058