Align overhaul scope and catalog lifecycle

[kim-em]

Summary

• reduce PLAN.md to the retained product scope and point execution at the authoritative completion documents
• update the mutable execution runbook with the verified disabled-state baseline
• rename the neutral catalog group to open-problems
• restore both reviewed software-verification entries to draft with append-only correction history

Validation

• python3 scripts/validate_catalog.py --base-ref origin/main
• python3 -m unittest discover -s tests/python -p test_*.py
• lake exe lean-eval validate-manifest --structure-only
• lake exe lean-eval check-problem-build for both software-verification modules
• all four Lean unit-test executables
• action-pin audit, Python compile, and git diff --check