Require regime-aware donor backend for PE rebuilds

[MaxGhenis]

Summary

• switch the PE-US-data rebuild profile default donor backend from qrf to regime_aware so release candidates use chained MicroImpute donor imputations
• fail closed when a PUF support clone rebuild is launched with a legacy donor backend such as qrf or zi_qrf
• mark the old zi_qrf next-run plan as superseded for release builds
• fix the checkpoint resume test fixture to represent completed stage manifests with no missing required outputs

Tests

• env -u UV_FROZEN uv run --python 3.13 --extra dev --extra policyengine ruff format src/microplex_us/pipelines/pe_us_data_rebuild.py tests/pipelines/test_pe_us_data_rebuild.py tests/pipelines/test_pe_us_data_rebuild_checkpoint.py
• env -u UV_FROZEN uv run --python 3.13 --extra dev --extra policyengine ruff check src/microplex_us/pipelines/pe_us_data_rebuild.py tests/pipelines/test_pe_us_data_rebuild.py tests/pipelines/test_pe_us_data_rebuild_checkpoint.py
• env -u UV_FROZEN uv run --python 3.13 --extra dev --extra policyengine pytest -q tests/pipelines/test_pe_us_data_rebuild.py tests/pipelines/test_pe_us_data_rebuild_checkpoint.py
• env -u UV_FROZEN uv run --python 3.13 --extra dev --extra policyengine pytest -q tests/pipelines/test_regime_aware_donor_imputer.py tests/test_variables.py tests/test_pe_source_impute_specs.py tests/test_pe_source_impute_engine.py tests/pipelines/test_zi_qrf_backend.py tests/pipelines/test_donor_imputer_negative_preservation.py tests/data_sources/test_scf_net_worth_components.py -k "imputer or regime_aware or columnwise or donor_imputation_block_specs or pe_source"