Map Arch SSI consumer facts

[MaxGhenis]

Summary

• map Arch SSA SSI recipient-count and payment-amount consumer facts into Microplex targets
• preserve SSI category constraints as model filters for aged, blind, and disabled recipient controls
• add a regression test covering national category counts and state payment/count facts

Validation

• uv run --python 3.13 --extra dev ruff check src/microplex_us/targets/arch.py tests/targets/test_arch_facts.py
• uv run --python 3.13 --extra dev pytest -q tests/targets/test_arch_facts.py

Context

This prepares Microplex to consume exact SSA SSI detail records from Arch without treating source-dataset diagnostics as model variables.