feat(report): add finding verdict boundary

[stacknil]

Summary

• add verdict_boundary to Finding and JSON finding output
• advance report artifact identity to loglens.report.v2 / schema_version 2
• update report-contract snapshots, README example, rule catalog, report artifact docs, quality gates, and changelog

Validation

• cmake -S . -B build
• cmake --build build
• git diff --check
• ctest --test-dir build -C Debug --output-on-failure
• privacy/secret scan over changed files