Fix Python decorator argument references

[Widthdom]

Summary

• Capture callable symbols used inside Python parameterized decorators and composed decorator chains.
• Avoid polluting call graph edges with non-call keyword configuration values while still recording callable keyword values.
• Add regression coverage and a bilingual changelog fragment.

Validation

• dotnet test tests/CodeIndex.Tests/CodeIndex.Tests.csproj --filter "FullyQualifiedName~ReferenceExtractorTests"
• dotnet build CodeIndex.sln -p:UseSharedCompilation=false
• dotnet ./src/CodeIndex/bin/Debug/net8.0/cdidx.dll status --check --json
• Adversarial review: two rounds completed; both actionable findings addressed.

Documentation / Changelog

• Added changelog.d/unreleased/2055.fixed.md.

Follow-up Candidates

• None.

Fixes #2055