test(report): lock golden report fixtures

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Summary

• add journalctl CSV golden fixtures for report contract coverage
• enforce full-file report.md and report.json snapshot comparisons
• document that parser or rule changes must update report snapshots explicitly

Validation

• git diff --check
• cmake -S . -B build
• cmake --build build with sanitized Path/PATH environment
• ctest --test-dir build -C Debug --output-on-failure