Add pre-calibration eCPS export schema checks

[MaxGhenis]

Summary

• derive the five eCPS-persisted inputs that the Gate-1 CPS-spine artifact was missing (fsla_overtime_premium, has_itin, has_tin, in_nyc, meets_ssi_disability_criteria)
• add a schema-only export-column resolver so saved PE entity tables can be checked before calibration/materialization
• add --entity-tables and direct-override support to microplex-us-check-export-columns
• add an optional rebuild checkpoint flag to fail the pipeline at the post-imputation/pre-calibration stage when the eCPS export contract would fail

Validation

• uv run --python 3.13 --extra dev --extra policyengine ruff check src/microplex_us/__init__.py src/microplex_us/policyengine/__init__.py src/microplex_us/policyengine/us.py src/microplex_us/pipelines/check_export_columns.py src/microplex_us/pipelines/us.py src/microplex_us/pipelines/pe_us_data_rebuild_checkpoint.py tests/policyengine/test_us.py tests/pipelines/test_check_export_columns.py
• uv run --python 3.13 --extra dev --extra policyengine ruff format --check src/microplex_us/__init__.py src/microplex_us/policyengine/__init__.py src/microplex_us/policyengine/us.py src/microplex_us/pipelines/check_export_columns.py src/microplex_us/pipelines/us.py src/microplex_us/pipelines/pe_us_data_rebuild_checkpoint.py tests/policyengine/test_us.py tests/pipelines/test_check_export_columns.py
• uv run --python 3.13 --extra dev --extra policyengine pytest tests/policyengine/test_us.py tests/pipelines/test_check_export_columns.py -q
• Gate-1 post-imputation checkpoint schema check: 246/246 required columns present, 0 forbidden columns present
• Gate-1 sidecar H5 export check: 246/246 required columns present, 0 forbidden columns present

Gate-1 comparison note

The fixed export surface passes the contract, but MP does not yet beat latest local eCPS on the primary sound comparison. Matched 41,314-household symmetric-refit holdout comparison against latest local eCPS gives MP loss 0.4294876907206762 vs eCPS 0.1726525197190867; eCPS refit recovery passed.