fix: scope drift issue closed-state dedup

[NocodeMrLi]

Summary

• Keep deterministic [Drift] issue dedup open-only so a future same-rule drift can still notify maintainers after an older issue was closed.
• Keep [Drift-audit] verdict dedup across closed issues to prevent resolved NO_ACTIONABLE_DRIFT duplicates from re-opening weekly.
• Add regression assertions for both call paths.

Verification

• python3 -m unittest tests.test_release_quality_boundaries.DriftWatchBoundaryTests tests.test_release_quality_boundaries.DriftAuditBoundaryTests -q
• python3 -m unittest discover -s tests -q
• python3 scripts/validate_suite.py .
• python3 scripts/check_i18n_readme_structure.py .
• python3 scripts/scan_sensitive_content.py . --format json
• git diff --check
• python3 scripts/drift_watch.py --platform-dir wechat --no-llm --output /tmp/mpes-current-wechat-drift-after-dedup-scope.json