Expose and persist PolicyEngine bundle metadata

[anth-volk]

Fixes #356

Depends on PolicyEngine/policyengine.py#349 for runtime availability of policyengine.bundle, and therefore transitively on PolicyEngine/policyengine-bundles#4.

Implements the API-consumer side of the bundle completion plan.

Changes:

• Adds a bundle metadata service and GET /metadata/bundle.
• Adds POLICYENGINE_BUNDLE_STRICT startup option.
• Records bundle metadata on new simulation rows and exposes it in simulation responses.
• Adds an Alembic migration for simulations.bundle_metadata.
• Updates direct PolicyEngine package pins to the current 4.4.2 bundle set.

Validation:

• uv lock
• uv run python -m py_compile changed Python files
• uv run ruff check changed Python files
• uv run pytest tests/test_bundle_metadata.py tests/test_health.py