Materialize Stage 12 report output variables

[anth-volk]

Fixes #695

Summary

• resolve a typed, country-aware output plan once per Stage 12 report
• apply the same plan to baseline and reform workers before calculation
• validate child artifacts against the plan before aggregation
• support cliff reports and preserve labor-supply policy metadata

Testing

• make test
• focused Ruff checks for all changed files
• focused Pyright checks for changed contract and executor modules
• full simulation-entry Pyright

Repository-wide Pyright still reports unrelated pre-existing errors outside this change.