Reinstate PolicyEngine v4 simulation runtime

[anth-volk]

Refs #434

Summary

• Reinstate the simulation API runtime path for policyengine.py v4.
• Resolve policyengine.py bundle dataset metadata through the release manifest and normalize PolicyEngine HF dataset artifacts to their GCS runtime equivalents.
• Preserve resolved bundle metadata in gateway submit/status responses and worker runtime payloads.
• Consume the published policyengine==4.12.1 release, which adds gs:// runtime dataset materialization.

Bundle Status

• policyengine.py: 4.12.1
• policyengine-core: 3.26.1
• policyengine-us: 1.700.0
• policyengine-us-data: 1.115.5
• policyengine-uk: 2.88.20
• policyengine-uk-data: 1.55.10

Validation

• cd projects/policyengine-api-simulation && uv run pytest tests/ -q
• cd projects/policyengine-api-simulation && uv run pytest tests/test_policyengine_dependency_source.py tests/test_release_bundle.py tests/gateway/test_endpoints.py tests/test_simulation_output_builder.py -q
• cd projects/policyengine-api-simulation && uv run ruff format --check src

Note: uv run ruff check src tests still reports the intentionally retained unused export_ot_to_console import in main.py from the commented console-export pattern.